Why is there a ? next to my puzzle rating?

Why is this?

maybe because it is very high, and the system does not know if it is accurate.

I don't think this is the case as then other users see only "?" without a number in the left column. And with the number of puzzles done in last few days, high rating deviation doesn't seem likely either. Unfortunately the rating deviation is not shown for puzzle rating so that we cannot know for sure.

There are also players with a 3000+ puzzle rating. The ? was there at about 2250. Maybe I gain faster rating points than that more difficult puzzles in 2250-range are offered by the system. I did 1700 "mate in 1" puzzles... Still not sure why ? is there.

There are some rules that if your puzzle rating is too high compared to your game ratings, it's considered "dubious" and hidden from other users. But these shouldn't apply to you yet (only if the puzzle rating is over 2500) and, as I said, in such case only "?" without a number is shown in the left column (for other users) which is not the case (I can see "2270?" in your profile).

See e.g. lichess.org/forum/lichess-feedback/hidden-puzzle-rating#5

Thx for the link and the 'code'. Now I sort of understand. I don't mind the ? next to my 2270 puzzle rating.