For me, the drills are frustrating and bordering on worthless as a standalone section. After the first few easy ones, there is very little explanation for the underlying principle that one should apply. Several of them seem impossible without the player seeking out independent material for guidance (i.e., books, articles, and web content not provided by chess.com).
But my main frustration is the omnipresent chess computer telling me immediately when I've made a bad move. Or worse, the computer itself hinting me to make bad moves. Seriously, it will lead me into draws and stalemates and sometimes even recommend a move only to tell me that it was a mistake after I've followed its recommendation.
In my opinion the drill section on chess.com is great. You can study endgames, checkmates, mastergames etc. It's really helpfull to improve your chess skills. Also a nice side effect is gaining lots of Elo-points.
My focus for this topic is mainly on the endgame section.
Furthermore I watched many, many video tutorials on this site in the lesson section and on youtube. At this point I want to recomment some of the content creators:
I really enjoy this content.
In addition to that a book recommendation is Jeremy Silman: SILMAN'S COMPLETE ENDGAME COURSE.
In his book he is categorizing different endgames for players in the 1000-2400 ELO section.
Now my suggestion for improving the drill section is following: