I have been executing VMs under Workstation 12 running on Linux Mint 18.3. All my VMs from Windows 2000 to 10 Enterprise and macOS 10.11 to 10.14 run fine and I can get them into full screen mode.
I have uninstalled 12 and installed 15. All VMs work well but full screen is greyed out. I tried several things but to no avail.
So I installed Workstation 15 in a Windows 10 pro VM and the exact same VMs can now be set into full screen mode running in this Windows VM. This indicates that the VMs with tools installed are O.K.
Why is it that these VMs can enter full screen mode under Workstation 12 running on Mint 18.3 but not the newer 15?