Thank you. With that I am now able to logon. However, didn't get past first page without confronting another issue. Here is a screenshot of the top part of the page displayed immediately after successful logon. It seems to be saying I now need to run setup. Given the problems I've experienced that creates some skepticism. In this case I am able to backup both the DB and website files which I have done. Would running setup be recommended by those with more experience than I have? It does look like it is expected that this can happen normally but I'm certainly not someone qualified to say "I know what I am doing!".
About messages like that in general please read:
https://www.zenphoto.org/news/re-running-setup-files/
The load of files listed and the "copied over an unknown release" are a downstream issues of the "weird" behaviour/issue you experienced on your server. Re-running setup may cause you the same troubles again.
That all needs to be solved somehow as you likely need to run setup on the next update and you may see these message on other occasions as well (if the server itself got an update). 1.6.5 is around the corner so to speak. As already mentioned all that is not the usual behaviour. Sadly I have no proper idea about that right now.
Both the DB and website files have now been migrated from my hosting service to my test system. After some minor configuration adjustments the test site was accessed and produced the same result reported above regarding the need to redo setup. With nothing to loose here it was decided to go ahead and elect to "Run setup". That appears to have been successful and this new test site seems to working fine. However, very little has yet been done but no apparent errors or issues at this time.
It might be worth pointing our that this new XAMPP supported testing site appears to be using "MySQLi" just fine. Still don't know what the warning about "MySQLi not connected" meant when first trying to run an initial setup on this same XAMPP system.
Thanks so much for the help. Remains to be seen if this does what I want but I now have something to work with. That would not be true absent the assistance provided herein.
Also, it looks like the normal default is to have site in "Maintenance Mode". In that, administrator needs to logon on "Open" the site. Might make more sense to say "Site has no content yet" given that it does take some administration to create some. Appears as though there is an option, that does need to be set by an administrator, to have the site "Open" automatically after setup runs. This finding appears to explain some of my prior experience. It would have been good to know about that when performing an initial installation.
The setup re-run request internally updates a kind of "system signature" and acts as warning for you as the owner that things change. For example a PHP version update or a MySQL update. Updates from PHP 7 to 8 can break things as can do MySQL 5 to 8 and similar. If they are serious is up to you.
Also, it looks like the normal default is to have site in "Maintenance Mode".
After running setup the site is in maintenance mode because you may have just performed an update you may want to test before opening it to the public. You can change that default.
Yes you have to be logged in for that but you need to be that if you are running setup anyway.
That the mode is enabeld is mentioned here: https://www.zenphoto.org/news/installation-and-upgrading/