What explains this sudden growth and the sudden decline of Linux in Ukraine?

Do we even know that there was a sudden growth or decline of Linux? This is a percentage graph. It is not very useful without also knowing the total number of users over that time. Could be that a massive amount of users stopped over that time, but for what ever reason fewer using Linux did than Windows did. Or if there was a massive increase it could be from bots or similar attacks. These graphs are very hard to draw any conclusions from due to what they are and how they were collected (which I believe is basically what user agents report on some websites) without a lot more other information. All we really know is that the market share for webtraffic started reporting more Linux based user agent strings (or what ever they use to tell) in relation to windows ones for a time before normalising again.

The one Ukrainian Linux user without an adblocker started visiting a website that still has a statcounter widget on it, but he got tired of it after a while and stopped?

Looks like a sampling error.

Steamdeck drone controllers?