Fusion menu > Windows > Merge All Windows
The macOS should be 10.12 and above.
The virtual machines should be in single window mode.
That worked. Thank you.
Part of the problem is that I was searching for "tab" or tabs" in the documentation...and nothing. However, now that I know that it's "merge" that I'm loo0king for, I searched the Fusion 10 User Guide for that word...and nothing.
Again, thank you for your help.