Late last night I decided to see if the T4 package and the Purity IV package, I liked Purity III when I used it and wanted to get Purity IV, would actually install as standalone Joomla installs as my Joomla 5 would indiciate they would when trying to add these.
They both started as a Joomla 5 installation. Purity IV went all the way through installation of Joomla 5 with Purity IV termplate, creating the database and only has a JSON error after installation when clicking on the buttons to either load the front end or backend.
The T4 framework started the same way, got the installation for Joomla 5, went through the process to create the database, but that install failed with errors and never completed the database creation.
Joomla 5 correctly saw both of these as installation packages of Joomla and can't be add-ons to Joomla. With an existing Joomla installation, I can not use these, I like the T4 framework and Purity is the starting template I like to use.
My experience with Joomla goes back to version 2 and my first online use was using Joomla 3 and T3 framework and Purity III to start and then built my site off that.
It would appear that I might have go back to older versions and try to upgrade to Joomla 5 and T4 and Purity IV. But, if they are actual install packages and not extensions, then I don't see that being possible either.
Anyway, though I'd post an update of what I have tried so far on this issue. I'd like to start fresh with the latest versions of these so I can bring my website back online.