Thanks for the quick answer and for accepting and implementing user suggestions (that’s certainly not something everyone does). Therefore, thumbs up.
Good playing CPU-opponents really would be a fantastic feature, though it seems tricky to pull off, in "Puzzle Bobble" style games on a 8bit computer like the C64, I guess. Unfortunately, on the C64, none of the existing clones of this puzzle-game includes CPU-opponents so far. Perhaps because it's difficult to implement a really good playing CPU?
On the other hand, there's a great "Puyo Puyo" clone named "Oy Up" on the C64 and this game actually features well-playing CPU-opponents. And the "Puyo Puyo" game-mechanic isn't exactly simple either, if you really want to play well. So, it's possible obviously. Also in other C64 puzzle-games like for example "Dr. Maria", CPU-opponents would be a fantastic thing to have. 16bit puzzle-games (on Amiga, MegaDrive, Atari-ST, SNES, PC-Engine) often have something like this, while in 8bit puzzle-games, you mostly don't have CPU-opponents, sadly. But for example the Game-Boy "Puzzle Bobble" games are surprisingly good and they have CPU-players and these are also acting good in gameplay, when you choose "hard" mode in these games.