You may have activated it the second you died, which happens to me literally millions of times, then you respawn and waste a heal because you didn't notice it's queued. Would be nice if you could somehow activate that you can't queue items while dead, as it would prevent this from happening.

It's just lag. The moment you see your opponent shooting isn't when they actually shot, there's quite the delay. It takes some time for the server to register what's happening; in cases such as the ones you described, it registered your opponent's action first. But in general, if you and your opponent shoot at the exact same time in your POV, your opponent's shot is landing first.
Would be quite helpful to be able to see what everyone's ping is to be able to handle such situations. Lots of competitive games do this already. Even in Minecraft you can roughly see how good each player's connection is.

I can't guarantee whether this works, but try this: go to where you have Tanki installed. You should be able to get there by right-clicking your Tanki Online shortcut and then select "open file location". If you land in some folder that contains multiple different programs, do that again, and you should land where you have Tanki installed.
The second folder there should be named "resources". In the resources folder, there's a file named "tankionline.json". If you open that, you should see a link after something called "loadURL". At the end of the link, it says "resources=https..." whatever. Replace everything after the "resources=" with the corresponding part of the link Opex provided that does it for you. Would be funny if this works ?
I tried doing this myself: cleared my cache, replaced the link, and at least my client is still launching without any problems.

Brutus isn't supposed to not use supplies at all, it's using 1 upon activation. Drones that boost a specific stat further, for example Booster, uses 5 double damage upon activation since it's boosting damage further, but only 1 of the others.
What drones do is boost the efficiency of supplies. If you have a drone equipped that is not upgraded at all, double damage isn't actually doubling your damage, it's giving you only a 50% increase (same for the others, double armor is increasing armor only by 50%). The further you upgrade any drone, the more % you will gain, totalling out at 100% efficiency eventually.
Brutus is the simplest and cheapest drone, which only gets you to 100% efficiency for each supply. Other drones however, like Booster, give you +100% for every supply besides the one they boost further. In Booster's case it's damage, so it actually gives you +125% damage, but for that you waste 5 supplies whenever you activate double damage, instead of 1.

My friend, if your or any profile is not showing, it just means it's set to private in the in game settings. Log in into the game, go to settings, then security, and uncheck "Hide your profile". May require some minutes for the system to notice the change, but eventually, you should be able to see your profile.

To report someone via video, you have to go to the Russian forum under the section marked by the arrow: Then, create a topic in the underlined section, post your video and describe the crucial timestamps. You can write in English.

For how long have you not logged in? Maybe someone else took your nickname, in that case yours should have changed to r_nickname0 or similar. The number at the end represents how many times that nickname was taken, starting from 0. So, it could also be r_nickname1 or r_nickname2 etc.
Here you can check after how many days of inactivity a nickname can be taken: https://en.tankiwiki.com/Nicknames?attempt=1

This isn't a new bug, it's been around ever since Tanki switched from Flash to HTML5.
In Flash, you could reliably hit doubles with railgun when tanks were standing in a row, no matter which angle. Ever since they switched to HTML5 however, it often feels random whether you can hit everyone in a row or not. Been around for ages already, unfortunately. Seems like the game doesn't realize that there are tanks in a row.

no

Minor changes don't always make it into the patch notes

What you can do then is wait until the client updates I guess, check if the version number is going up every now and then. Might be that it won't update on its own since you can't start it apparently.
On Windows, you can check the version by hovering over the file that starts the thing, in my case it says 2.0.2.0

That may be because the polling rate of your mouse is set too high, usually it's set to 1000. This number shows how many times a second your mouse is updating its position, as far as I know. Depending on the mouse you have, you can lower the polling rate in the corresponding software, for example G HUB, if you have a Logitech. Set it to 500 or whatever and try again.
Otherwise, I don't really know how to change the polling rate.

Any forum moderator/administrator you will reach here will not be able to do anything for you. What you should do instead is reaching out to the game support under help@tankionline.com, they will surely be able to resolve your issue

That's a major problem in pro battles currently. Some battles that don't exist anymore are still shown in the battle list and seem like you can join them, but if you join you get disconnected. Also, if you're unlucky and get stuck in such a battle, your account will be gone until the next server restart, since you can't do anything to remove it from that bugged battle.
It's not a problem on your end, it's the servers having issues.

I feel like ever since the game switched from Flash to HTML5, there have been all kinds of problems related to tank-to-tank interactions. Pushing became impossible as you always clip into the other tank, so blocking is also not possible. And now, with the new HD models, you can't even stay on top of someone, as you will slowly start falling into them at some point. It's ridiculous.
Hitting doubles also became very hard ever since they switched. When you shoot an opponent who is at the same height using Railgun for example, your shot doesn't go straight. It goes down a bit, as it seems that turrets aim for the center of the opponent's hull. So, as you can imagine, this makes it almost impossible to hit people who are standing in a line, as your shot lands in front of the guy who is standing behind their teammate, not hitting him. In Flash however, the shot just went straight, hitting everyone who was standing in a line. But in HTML5 it feels like 1 out of 5 shots do that. So hitting doubles is also completely broken.
To answer your question, looks like it's just ping-related, but also game-related issues as well. All we can do is hope for the devs to address these problems I guess ?‍♂️

It doesn't matter for how long you have been #1, if someone surpasses you he's ahead and he wins the challenge.
I'm pretty confident that the devs are competent enough to make sure that the player with the most stars at the end of the challenge, not before or after, gets the drone. Everything you earn (including stars) is logged, there is no way they could screw this up.

If there is a parkour event, it will be announced in a way that if you search for it, you find it.
If you try to search for any parkour event now, you won't find anything, so there is no parkour event currently

There you have it, because you have a lower end system. Many players have a low spec PC, adding rain or any other detail would just make the game require more performance to run. Low spec players would have even less FPS then.
You could of course argue about adding lower detailed rain, but it would still require more performance, and it would probably not look very good.

About playing in the Netherlands, check this topic:
What do you mean by you can't delete the Flash Player? It's discontinued and Tanki doesn't support it anymore. You should have access to the new HTML5 version via every browser, or by downloading the new client

https://ratings.tankionline.com/en/user/Cringey?

That's some weird bug, I guess. If you can't deal damage at all you can try self-destructing once, if it's still not working, try refreshing if you're on the browser or restarting your client