[mzltest]

What was interesting to me is that I was transferring four WP sites from one VPS to another.  Three had no issues, and they had default twenty thirteen WP themes on it that I updated with a child theme.  So looks like Wordpress themes are OK.  

For me looks like old themes that owners of the themes are no longer interested in, and have forgotten about, but are still popular any way, are going to be a real problem.  I have a few other Website backups that I "archived" a while ago, that are basically extinct now.  

Yes.But in many cases you don't have to make a dedicated support for newer versions as long as in your versions there is no DEPRACATED or NOTICE warnings. And maybe that's why some applications in PHP 5.6 era works with PHP 7.x .As for me since I made a simple pastebin myself that I once mentioned in shoutbox,my local environment is PHP 7.3 while the website environment is PHP 8.0.Most of the code works except that one function I used from internet which used to generate a fixed number of random characters,which I mentioned last reply.

Thanks for the feedback @mzltest.  I've got a few  hosting accounts, including shared hosting accounts.  There is one I value very much for always being up to date - Limitless Hosting - and not only does it have php 7.3 as the recommended php, but there are several versions to choose from in its panel.  Coincidentally, last night when I created a new Website with CyberPanel (a user account with @fitkoh) running on his VPSs from RackNerd, when you create the Website it gives you a selection of VPS 7 versions to choose from.  Courtesy of CyberPanel.

Yeah.Most hosting provide PHP versions from 5.6 to 7.4.As this is a new-stage release rather than maintaince the applications aren't ready for it and there are many uncompatibilities.And for this reason I believe the PHP 5.6 is provided for these old and maybe unmaintained scripts to work.

(Offtopic)

Aha.  Now that must be the reason for the problem in the first instance.  Nginx.  And yes, there were a Tower of Babel number of suggestions out there how to conf it.  I tried, but obviously was doing it in the dark - I didn't really know or understand what I was doing.  There was the var/www/httpd .htaccess suggestions and then the public folder .htaccess.  In the end I thought I may create a security issue when I didn't know exactly what the consequences were going to be. As Admin at Gigarocket we always discouraged members from using .htaccess as it's not that secure to Override "All" functions.  Silver lining is that I connected up with my CyberPanel Account, and am studying it presently for installing on my VPS 9.

Peraonally I think most applications prefer apache than nginx as they can modify the server settings in their working directory to fit the needs by themselves just using .htaccess however in nginx you need to ask the user to modify nginx.conf .