So, I successfully upgraded to Byzantium (not without problems, see Gnome not working after upgrade to Byzantium), but now the screen flickers annoyingly. I have updated the firmware (which worked last time, see Librem 13v2 screen flickers, and solution in Troubleshooting doesn't work) to BIOS 4.17, and also set GRUB_CMDLINE_LINUX=“i915.enable_psr=0” in the grub file (/etc/default/grub), but that doesn’t change the situation after reboot (I did “sudo update-grub” before rebooting). The flicker is still there.
It started when I upgraded to Byzantium, so I am quite sure it is not a hardware problem (it was not last time when I had this problem, in Jan 2020, actually with the same computer).
Any further ideas?