zhus' suggestion did not work for me.  I checked in Privacy and there was nothing to approve.

I uninstalled VMWare Tools, shut down and rebooted the guest, and reinstalled VMWare Tools.

I still only get the 1024 x 768 resolution.

If this helps, what happens is this. When I first boot the guest, the VMWare screen shrinks to about a 3"x3" square (just as happens with my Windows 10 VM).  Unlike the Win 10 VM, with my Mojave VM, the VMWare window stays at the small size after the VM finishes booting.  At that size, the resolution is great...matches my 27" iMac.  But if I resize the VMWare Fusion window, it grows proportionally (aspect ratio preserved), but, unlike the case with the Win 10 VM, it doesn't "flash" back to the correct resolution.  In System Prefs-->Display, only the 1024x768 resolution is there.

Anything else to try?