You can curate a specific collection. Want only Mate in 2 problems by Soviet composers from the 1950s? There is a PDF for that. Want Miniatures (7 pieces or less) to solve during your coffee break? There is a PDF for that. You own the file forever; you aren't renting it from a subscription service.
A single Mate in 3 problem from a PDF studied for 30 minutes is worth more than 50 blitz puzzles solved in 5 minutes. chess problems pdf
Stop moving the pieces. Start thinking. Download the PDF. You can curate a specific collection