SOLUTION REPORT :

I solved this issue after following a suggestion from /u/w33d : running manually the command which failed.

So I did the following:

Restarted the VmWare Workstation installer and ran it up to the blank dialog box with OK button.

Copied the failed command below from vminst.log :

openssl.exe req -x509 -sha256 -days 365 -newkey rsa:2048 -keyout "C:\ProgramData\VMware\SSL\rui.key" -out "C:\ProgramData\VMware\SSL\rui.crt" -config "C:\ProgramData\VMware\SSL\hostd.ssl.config"
Opened a command prompt at C:\Program Files (x86)\VMware\VMware Workstation , pasted the command line from #2 above therein, and ran it.

A dialog box came up; since it had remained hidden when the same command was run from the installer, this was THE KEY to the solution ! It stated :

The program can't start because api-ms-win-crt-runtime-|1-1-0.dll is missing from your computer. Try reinstalling the program to fix this problem.

5.. Some Googling, chose going to https://www.itechgyan.com/api-ms-win-crt-runtime-l1-1-0-dll/ . Adapted the recommendations and did what follows on #6.

6.. Control Panel\Programs\Programs and Features -->

“Microsoft Visual C++ 2015 Redistributable” [there were actually TWO - x64 & x86] - 14.0.24.215

Change ---> Repair

got an error, seemingly due to "another installation is in progress" - which evidently was Vmware's main one, still paused.

7.. Hit OK button on Vmware install's blank dialog box , let everything roll back.

8.. Found that both "Redistributables” remained installed, did the "Change ---> Repair" operation again on both - with success this time.

9.. Despite Windows Search NOT finding any 'api-ms-win-crt-runtime-|1-1-0.dll' in the system, some more googling & youtubing led me to manually find TWO files with this name, on C:\Windows\System32 and C:\Windows\SysWOW64 .

10.. EASTER EGG #1 : found that 'C:\Windows\SysWOW64' is subject to some internal system redirection and should NOT be added to the PATH variable.

11.. EASTER EGG #2 : found this quite surprising monstrosity, which I was totally unaware of : https://stackoverflow.com/questions/949959/why-do-64-bit-dlls-go-to-system32-and-32-bit-dlls-to-syswow64-on-64-bit-windows

12.. Restarted the VmWare Workstation installer, which this time ran flawlessly from beginning to end.
Thx everybody, and /u/w33d in particular. :))