Seems, that there is a trouble with Lightdm in last release. When the screen is locked due to inactivity, you cannot log in. When entering the password, after each letter the screen flashes and does not allow entering the password. I have lightdm-gtk-greeter on my system.
Maybe you can try this first and see what happens.
Make changes in /etc/lightdm/lightdm.conf to the followings:
$ sudo groupadd -r autologin
$ sudo gpasswd -a user-name autologin
replace xfce with your desktop
this is reported all over the place… i would like to try getting to the bottom… but would need some logs to see.
And i do not have this issue here at all… but using default slick greeter from install…
Also curious what is used to lock the screen… as we do not install light-locker per default.
I had troubles from the start. Because of this I changed slick greeter to gtk.
and is light-locker installed? plus what DE is used …?
yay -Qs light
If it is XFCE4 … it will be not lightdm at all zthat locks the screen it is
xfce4-screensaver what is used on xfce4 per default…
So you can go replace it with light-locker to see if this solves your flicker issue…
yay -Rc xfce4-screensaver
yay -S light-locker
reboot and check…