I’m not tech savvy and have noticed that many streaming sites are .ru, and as someone located in Finland, I want to make sure if they are dangerous to use.
tl;dr:
RussiaMITM can very easily redirect any traffic to any .ru site to anywhere they want.
Yes, that’s true, but more generally speaking, an external attacker would need to first gain access. The governments who control their national TLDs already have that access. Could the UK do the same thing with the co.uk TLD? They could, but the UK government seems more trustworthy on that point than does the Russian government.
OP asked specifically about the “safety” of .ru sites. I answered that question in that context.