MUTTER_DEBUG_FORCE_KMS_MODE is not having the desired effect because I forgot GNOME 42 uses a different variable. Please try:
MUTTER_DEBUG_ENABLE_ATOMIC_KMS=0
in /etc/environment and reboot.
Similarly, MUTTER_DEBUG_KMS_THREAD_TYPE will have no effect because that feature doesn't exist in GNOME 42. But I hope that MUTTER_DEBUG_ENABLE_ATOMIC_KMS=0 will help.
MUTTER_ DEBUG_FORCE_ KMS_MODE is not having the desired effect because I forgot GNOME 42 uses a different variable. Please try:
MUTTER_ DEBUG_ENABLE_ ATOMIC_ KMS=0
in /etc/environment and reboot.
Similarly, MUTTER_ DEBUG_KMS_ THREAD_ TYPE will have no effect because that feature doesn't exist in GNOME 42. But I hope that MUTTER_ DEBUG_ENABLE_ ATOMIC_ KMS=0 will help.