OK
I did it and seems to work fine, upgraded to 8.2.23 (actual latest of the 8.2 branch, I thought being a bit conservative might be fine, so I did not opt for the 8.3 branch yet)
I also understood what fooled me into not finding the very easy proper solution using CWP GUI just as is...
The PHP-FPM method is used to have multiple PHP versions in such ways so to be able to easily maintain up to date and choose/switch at wish with a few clicks one of the many PHP versions for the domains' webservers in order to accommodate the various software needs. That is simply awesome!
When in CWP the PHP-FPM system is activated in the PHP Switcher panel appears a warning telling the following:
WARNING! This PHP versions are not active as you have forced PHP-FPM here!
You can use PHP-FPM selector per version configuration and modify WebServers for each domain/subdomain if you want to use a custom PHP-FPM version.Somehow that warning did let me think that the PHP Switcher panel is not active and not to be used when PHP-FPM is in use!
That misunderstanding one can fall into is due to the very first sentence of the warning: "This PHP versions are not active as you have forced PHP-FPM here!"
That warning let one think that when PHP-FPM is active there is nothing to do in the PHP Switcher panel, also there is no note telling that the PHP switcher can be anyway used to change the main server PHP version even if PHP-FPM is active.
Furthermore nowhere is written that the main server PHP version cannot be changed via the PHP-FPM manager.
That first sentence in the warning message should be changed into somewhat more accurate that do not tell people, "leave this place as you can't use this until you use PHP-FPM" ^^
Maybe should be somewhat like this: "If PHP-FPM is active this PHP switcher can be used only to change the PHP version of the main server, cannot be used to change the PHP version of the webservers...".
So far so good, I cleared out an "enigma" ^^, to me looked too strange that could not be possible to setup different PHP versions for the main server using the CWP GUI itself, finally I know why I could not figure it out. This was a funny event
^^
Thank you for the very useful hint, very appreciated.