I think we need another Category for GPD systems. The touch screen failed to work on my system too after I upgraded to 20.04., wipe the drive and went back to 19.10., now works.
I'm not running Ubuntu MATE; I run OpenSUSE, but I can confirm that my GPD P2 Max also has this Goodix touchscreen issue.
The dmesg output is:
Oct 22 19:11:04 marauder kernel: Goodix-TS i2c-GDIX1002:00: supply AVDD28 not found, using dummy regulator
Oct 22 19:11:04 marauder kernel: Goodix-TS i2c-GDIX1002:00: supply VDDIO not found, using dummy regulator
Oct 22 19:11:04 marauder kernel: Goodix-TS i2c-GDIX1002:00: i2c test failed attempt 1: -121
Oct 22 19:11:04 marauder kernel: Goodix-TS i2c-GDIX1002:00: i2c test failed attempt 2: -121
Oct 22 19:11:04 marauder kernel: Goodix-TS i2c-GDIX1002:00: i2c test failed attempt 1: -121
Oct 22 19:11:04 marauder kernel: Goodix-TS i2c-GDIX1002:00: i2c test failed attempt 2: -121
Oct 22 19:11:04 marauder kernel: Goodix-TS i2c-GDIX1002:00: I2C communication failure: -121
Oct 22 19:11:04 marauder kernel: Goodix-TS: probe of i2c-GDIX1002:00 failed with error -121
What's interesting is that despite it using OpenSUSE Tumbleweed, it still has the same issue reported here. I'll make a post on the GPD Support forum at some point, but I just wanted to mention that those who are experiencing this bug are not alone
Hopefully we can get it fixed soon... my touchscreen works fine on Windows.