So I was trying for a long time to get OpenGL working on an Odroid XU4 (mini PC - similar to RaspberryPi4); and here the good news. I just made it work.
I’ve set up a new boot SD Card and instead of using the manufacturer’s (hardkernel) Ubuntu 20.04 image; this time I tried the Arch-Linux instead and followed these instructions: ODROID-XU4 | Arch Linux ARM
then installed lightdm display manager with mate desktop. It seems very stable and very responsive.
I then followed the build instructions Compiling On Linux · mixxxdj/mixxx Wiki · GitHub
the main difficulty was to get all the libraries installed and compile some of them. In general, arch-linux offered most of the missing libraries (and there weren’t 10 different versions as in Ubuntu, just one).
I still need to fine-tune the system getting RT IRQ working and setting up my 7" touchscreen - I’ll use this thread for updates.