Hi! I can't log in to my account in the FAF client! The FAF website opens up for me and asks me to enter it, but after I do this, I am asked to link a steam account. After I tried to do this, it tells me that my Steam account is already linked. I can't do anything else and I can't enter the game in any way. 
you linked this account already to user with name ...
The most likely answer is this: Some time in the past (any time in the last 10 years), you registered an account with FAF, with the username "Octane"
A search within the FAF client shows that the Octane account was used to play games in FAF from December 2018 to basically the present (a couple weeks ago). Have you been playing FAF all this time?
I think you created a new account in the last 2 weeks or so. You need to log in to FAF using your Octane login. not this new account "Neulovimiy."