Well, it seems that no one is interested in the topic. Well, I bring you some progress. I confirm that it is necessary to flash the graphics card with the appropriate ROM, it does not automatically detect the 64MB. I have changed the VRAM and the image appears undefined. Tested with all 4 chips, to rule out defects. I have re-soldered the 32MB ones, and the image is back.
We need some ATIflash for Mac OS9 or OSX that allows us to download from 1.5GHz and load at 1.25/42GHz. Unless the ATI ROM is stored alongside Apple's Boot ROM, then you will need to dump that content and add it back. I have a TL866 programmer and adapter for that chip, but someone should desolder and read the Boot ROM from their Mini 1.5GHz with a programmer.
edit: It is possible that the 32MB chips instead of the 16MB ones did not work because the original ones are HY5DU283222AF at 2.5V and the ones I put in from the PowerBook are HY5DS573222AF at 1.8V. Perhaps that excess voltage has caused the incorrect operation. Difference between "DU" and "DS", I just noticed the difference.
edit 2: There were some minor graphical glitches, and I thought that by reflowing they would be solved, but my surprise was that after the reflow with the two 16MB chips I now have the same symptoms as with the 32MB chips!! Those 32MB chips came from a motherboard for parts, and perhaps they were damaged, or were damaged when removed, due to excess heat. Soldering memory chips costs much more than a CPU. Now I have found both 16MB and 32MB used chips, but they will take a few weeks to arrive. I have to find out the VRAM voltage because the 32MB ones are still 1.8V and the 32MB ones are 2.5V. Both 300MHz. I would be grateful if someone could provide me with the schematic of the Mac Mini G4: 820-1652-A, because I can't find it.