I wish the puzzle themes could get fixed. Basically any puzzle that showed a passed pawn or had a vague pin anywhere was tagged as such whether it was relevant to the puzzle or not. I do some puzzles every day but I wish that I could do custom puzzle themes for focused topics. If it's not one of the mate in X themes it can be pretty hit or miss.
I feel like random puzzles is important but for learning different tactics, random puzzles is like trying to learn math concepts by just randomly looking for a problem anywhere in the textbook. Chess.com really would help out improvers by fixing the themes to allow for drilling tactical concepts easier.
lichess has an entire database of specific motif problems, and so does chesstempo
the internet is too vast to not find apt resources for improvement, free or not
the key to getting better at this game is to practice until your brain melts and your hands fall off