On the OP:
There seems to some issue with patches which causes the screen to blank after activation.
Specifically, Jolla has apparently broken all “overlay apps” in this release.
On a freshly flashed system:
I installed Patch Manager but no patches.
Installed “Battery Overlay”
On activation of Battery Overlay, the screen blanked.
On reboot, Patch Manager autostarted Battery Overlay and blanked screen