I forgot to put the actual tips:
Every game I play ends with a board filled with blocks in a group of 1
Yes! You're so close to getting really good at the game! So you know now what poisons the well. Then the next insight is that it's more important to not poison the well (even if it doesn't score immediately) than to score (if that means leaving junk). Doctor Mario has a similar quality to this where each pill has two halves you need to manage efficiently and economically but that's easier in many ways since those pills only have two halves and there are only three colors. Tetris Flash a.k.a. Tetris 2 also comes to mind. Mixolumia is harder than those for those reasons. In exchange we can clear blocks in two ways (making lines of at least three length or rectangles of at least 2 × 2 size—and rectangles with protrusions also get cleared because those get detected as lines) and we can split up the blocks, they fall apart after landing which can be a hindrance or a huge help, depending.
I usually die on the endless mode (my score is around 2 mil but I only just started playing) because I get confused near the top when the "ghost" overlap the real block. On relax I don't get as confused by that since it's slow and I can dig down again to a well that's like 20% full and then keep it around more or less half full indefinitely.
Not to come across as someone who thinks she's smarter than other people 🫢 I just played sooo much Dr Mario, Dr Luigi which like this gives you four blocks at a time, and Tetris 2, and this is the next level from those. Certainly harder! 👾
Learning to see connections "through" what's going to get deleted is not easy. It's like an https://senseis.xmp.net/?IshiNoShita in go or an x-ray attack in chess https://en.wikipedia.org/wiki/X-ray_(chess)
