Lichess thematic tournaments

I think thematic tournaments should be casual, so it doesn't affect our ratings when we play openings we aren't familiar with.

Better question, how are users able to create rated thematic tournaments?

I'm not sure if users can although lichess creates tournaments like lichess.org/tournament/gJnrsqad which is rated and thematic.

It's your choice to join a thematic tournament. They should be rated, if you don't want to play that particular opening then don't join the tournament.

what if he wants to play it but causal , and if he creates a causal thematic tournament , I'm pretty sure that it won't have many participants

I want to play the opening and learn it although I don't want to lose my rating

In a thematic tournament, you should open Stockfish on that position and go through the moves beforehand. Really, I don't know what else to say!

I think you can just do a casual game with the preset setup and that should be fine. Rated games simply give you an incentive to play your best. Moreover, the scheduled factor comes into play and it gives more reason for it to be rated. It is not about the rating at the end of the day, but the mindset during the game. If you do not feel you are ready to play then just make a casual challenge. Otherwise, if you want to challenge yourself, then go for the rated game and put yourself to the test.

@Cedur216 you can generate a FEN and paste it in the FEN box.