According to their announcement https://gtm.steamproxy.vip/games/551110/announcements/detail/1666769140384136354 they "added 10 new levels (unlocks after completing whole game)"

To complete the whole game (and get all the achievements) you must complete the secret final level, which appears when you have completed ALL of the other levels using the minimum number of moves (no more yellow blocks in the level overview).

I completed all the levels but there are yellow blocks, and if I sole the puzzles, the yellow blocks don't disappear.

To make the yellow blocks disappear, each puzzle must be solved using the "minimum possible number of moves" or the "fewest moves possible", which would be considered the "perfect" solution. At the top of the screen, there is an indicator to the left of the restart button that turns red if you have used too many moves.