Was the screensaver lock on the Mac or the Xubuntu guest? What version of Xubuntu? 

xubuntu screen lock, it is kernel 5.13.0-30-generic Ubuntu 20.04.4 LTS

This happening to me with fusion 12 and windows 10. Very annoying. Eventually it starts responding again. It started happening when I got my new iMac (intel based) and am running dual screens.

And it's MacOS that goes to screen lock.  After waking up I get the "to unlock your mouse push cmd ctrl" After a few minutes things are back to normal.

What's the host and guest config?  I've seen that when the host was starved for cycles.

iMac 27 inch 8 core intel I7 3.8Gh. 32GB memory. macOS 12.2.1

Fusion 12.2.3  3 of 8 cores dedicated to guest. Hmm I only have 8GB of memory allocated to the guest. But the rest of the computer is doing nothing so ...

Windows 10 guest. Up to date

Only thing running in the guest is Quicken windows (up to date). (Mac version of Quicken is brain dead which is the only reason that I use fusion)

This doesn't happen on my MacBook Pro (2018 vintage 16gb)

The two differences from the MacBook are that it has twice as much memory and more cores.

and dual screens

Shouldn't be a host starving problem.  If you're using unity or full screen mode, does it happen when in windowed mode?

One other thing - make sure you set 'prevent host from sleeping when screen blanks' in system preferences/energy, and set it to 'never' sleep.  Sleeping a host while a guest is running is something that doesn't always work (sometimes it does, but others it doesn't).

This problem has been less of an issue lately, but. not yet gone.

After the upgrade to 12.2.4 it happens every time.

To review. Windows 10 virtual machine. Mac goes to sleep. When I get back it is unresponsive. 

And in the upper right corner it says "to release your mouse press cmd-ctrl.  

Sometimes when I send a couple of control alt deletes it wakes up.

Today I walked away with nothing running but Windows 10. No apps. Quicken has nothing to do with it.

Really really annoying