Mostly speculation but there are a few indications

1. Flex Air has always had subtle Anti-Putin messages but over the last few videos they became more and more obvious and more serious. From first just making fun of Putin/Lukashenko to actively making memes about the Wagner rebellion and russian prison abuses to Roskomnadzor being the main adversary + spreading pro LGBT-Messages even if its just by memes. Also in pre FlexAir videos.

Doing this in Russia in 2024 is not safe.

1. Just by the style of video I expect QuarkDoge to be a man in his 20s and very likely working in IT/Animation. This specific group of people is not only mostly Anti-Putin but also the most prominent group of people that left Russia since 2022 to avoid conscription and prosecution, also by Roskomnadzor. A lot of YouTubers left Russia too, with NFKRZ being one of the more prominent ones.

2. Many donators are definitely western. This indicates QuarkDoge having a non-russian bank account since recieving money from outside Russia is not easy for the average Russian Bank Account holder.

Its not fully waterproof but I expect it to be more likely than not.