I found a thread exactly about this issue here.
Though I have no idea about what PSR is, disabling it by adding
GRUB_CMDLINE_LINUX_DEFAULT="i915.enable_psr=0"
to /etc/default/grub
then “$ sudo update-grub” and “reboot”
seem to fix the screen tearing, delayed rendering issue.
To check if PSR is enabled by entering
$ sudo cat /sys/module/i915/parameters/enable_psr
should return “0” zero.
Formerly, it gave me “-1”.