Your posts are not blocked by some type of filter. You have to have enough upvotes to post in mot Reddit subs or the sub moderator has to approve of your post.

It’s like you have to be chosen, do everything by their rules, and even write to some moderator personally about this problem

It is NOT like that. It IS that way.

This social network has long since ceased to respect freedom of speech

Reddit like a private entity has no obligation to respect your freedom of speech or provide you an avenue to practice your free speech.