This error is caused by BattlEye, and mainly occoures when you mess with a another game that has BattlEye Anti-Cheat.
Follow the upcoming steps to easily fix your game and continue grinding!!

The first step is to close the launcher in the following order:

Go to the folder where you downloaded steam, then👉

steam\steamapps\common\War Thunder\EasyAntiCheat

(screenshot in the next section)

In this folder you will find EasyAnitCheat_Setup.exe, open it👈

After you launched the app in ❗ administrator mode ❗ click on the following buttons:

You can now close this app and launch the game, no errors should occoure!

Thank you for reading this guide, if you feel so please rate this to help steam to reccomend this helpful guide to people needing it!