physlock VS waylock

When I resume after suspending, the tty prompt for physlock comes up, as intended. When I enter my password, though, it shows the desktop and lets me move around the mouse, but the keyboard does nothing.

I'm not familiar with the PinePhone, but since you're able to use fbkeyboard in VTs, it sounds like physlock might work for you. I just wrote a comment about it in another thread. Unfortunately it's not very amenable to customization.

I use and recommend physlock. It's the most security-focused screen locking utility I'm aware of. Upon activation, it switches out of the graphical session and into tty0 which helps mitigate both of your issues. It also locks TTY switching to prevent accessing a logged-in TTY while locked, which is something that I don't think most other screen lockers do.

I use physlock[0] which locks all of the ttys. I've had no issues.

[1] https://github.com/muennich/physlock

I meant that a standard of some sort is probably needed to handle both the desktop environment telling the display manager to lock the screen AND allowing said display manager to take over the screen and lock it. On Wayland at the moment I'm not aware of any screen locker that isn't part of the DE itself that works on GNOME or KDE (I only know of swaylock and waylock, and both require protocols that are only implemented by wlroots based compositors, at least according to Waylock's readme).

I only know about waylock, didn't try it though