... A VMware Fusion 11 problem, or an open-vm-tools-desktop package problem, or both?
Thanks to mykmelez for his/her input. Myself did not applied the /lib/systemd/system/open-vm-tools.service based fix as at close point of time I found mykmelez's hint then followed them.
Here Ubuntu 18.04 on Fusion 11.0.3 is used, host is 10.12, open-vm-tools are in use since long time ago (as soon as realized VmWare's notification about stock version deprecation)
Discussion in bug thread #1818473 (launchpad Ubuntu) were consulted and the decision was made to install open-vm-tools update from `proposed` repository.
Guest screen resolution problem seems to be resolved by that update in durable way. Update was made yesterday afternoon.
For open-vm-tools from `proposed` repo as first myself completed Ubuntu update in usual way.
Then `Pre-released updates (bionic-proposed)` option was enabled in Ubuntu Software & Update app, section Developer Options.
Software Updater was started.
Software Updater has found a long list of "proposed" fixes, all have been unselected in order to select just the item corresponding to VmWare Open Tools, there was one single item that kind on the list.
Update was completed.
Restart and check if it helps.
In the end Pre-released updates (bionic-proposed) option has been set back to disable.
User enjoys working screen resolution.