Hello again.
Today I found some time to play with my laptop again and I can report that I solved the trackpad issue. (As mentioned above I will deal with the audio problems in a different thread as soon as I proved that there is no hardware problem involved)
Just entering the grub arguments was not enough. I also switched dom0 updates to Unstable updates. But at least, I can use the trackpad now.
For other users with similar problems: This is my current GRUB configuration sudo nano /etc/default/grub applied via sudo grub2-mkconfig -o /boot/efi/EFI/qubes/grub.cfg. But I am unsure if just switching the update channel is sufficient.
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=false
GRUB_TERMINAL_OUTPUT="gfxterm"
GRUB_CMDLINE_LINUX="rd.luks.uuid=luks-0c65cb5e-d2d0-474f-af0e-89c65050b234 rd.lvm.lv=qubes_dom0/root rd.lvm.lv=qubes_dom0/swap plymouth.ignore-serial-consoles rd.driver.pre=btrfs rhgb quiet"
GRUB_DISABLE_RECOVERY="true"
GRUB_THEME="/boot/grub2/themes/qubes/theme.txt"
GRUB_CMDLINE_XEN_DEFAULT="console=none dom0_mem=min:1024M dom0_mem=max:4096M ucode=scan smt=off gnttab_max_frames=2048 gnttab_max_maptrack_frames=4096"
GRUB_DISABLE_OS_PROBER="true"
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX rd.qubes.hide_all_usb i8042.nopnp i8042.reset i8042.nomux i8042.noloop"
I have to thank you again for your time, help, and patience, szz9pza. I’m sure I couldn’t have solved the problem without your ideas.