I have rebooted, and tried installing the Spectacle snap, and Snap seems to be working so far.
Edit: tried launching Spectacle, and got this:
$ spectacle
WARNING: cgroup v2 is not fully supported yet, proceeding with partial confinement
spectacle: symbol lookup error: /snap/spectacle/140/usr/lib/x86_64-linux-gnu/libKF5KIOWidgets.so.5:
undefined symbol: _ZN9KLineEdit16returnKeyPressedERK7QString
Will try with another snap.
Edit: it seems to be just Spectacle, as I was able to launch Firefox.