"the" typically designates singular or a title.
Jesus Christ is THE son of God
Jesus Christ is A son of God
Do you see how the different article renders those subtly but completely different meanings? If Jesus is simply "a" son of God it implies that there are or could be other sons of God. It denotes more a type of status or categorization. THE indicates it as more of a title, for example "the heavy weight champ" specifies a specific individual, "a heavy weight champ" is more general and categorical. Saying about a specific day that "the day was rainy" indicates that that specific day was rainy. Just saying "a day was rainy" doesn't indicate which specific day. "injustice critic" unless it is a specific name or title as in channel "InjusticeCritic" would sound like "an injustice critic" as in a job or profession. "the injustice critic" is referring to a specific channel or person. If you were speaking generally, like "the job of the injustice critic" is speaking in that case specifically of the professional in that profession.
So OP with your phrasing I honestly could not even tell at first if you meant it as a channel or title of someone's job except
>It is a title of the russian youtube channel.
Saying it that way implies that this youtube channel has more than one title of name.
If it is the name of a channel you capitalize it or in case of internet things write it as is (like for example "moot" stole his mom's credit card, not Moot). If the name of the channel is simply youtube/watchrtw45t4st#injusticecritic I suppose, maybe it could go either way? I guess it would simply be "injusticecritic". If a screen name is CatSpoon you would say it's simply CatSpoon like "and this is Dmitri" not "the Dmitri" just Dmitri. Unless it was like a man of notoriety or someone you specifically meant to separate out, like "oh you mean THE Dmitri Dmitroslav is here?">>4851
If it has already been established that it is a youtube channel or screen name yeah. Or "the channel injusticecritic" or simply "injusticecritic on youtube"