The installer shouldn’t lose your settings – it tries hard to not overwrite – but not impossible. But after it’s installed, it shouldn’t lose all the settings.

One guess is that the config.xml file doesn’t actually have normal write permissions, so when you make all the changes inside Notepad++, it tries to save the settings, but cannot – I would have thought it would prompt you for that, but maybe not. Use Explorer to go to %AppData%\Notepad++\, and right click on config.xml, and check the permissions, to make sure your normal user has write permission to the file; and also make sure you aren’t running Notepad++ As Admin – it would have Administrator in the title bar, and list it as Admin Mode: ON in the ? > Debug Info – because maybe your system is set up so Admin cannot write to your AppData directory.

Another guess is that you have two copies of Notepad++, and when your settings are changing, it is because it’s using a different copy of Notepad++, pointing to a different config location. Use Windows search to look for notepad++.exe, and see if it finds more than one copy. (If you have multiple drives, make sure you check them all.)

I thought or was told that the the app’s preferences etc. loaded from the Session file?

Nope. Settings are stored in config.xml. The list of open files is stored in session.xml

I can’t remember where you can change the setting or edit a line so more items are remembered in the Find What window, can you please tell me how to set it to (12)

It’s a Preference for Advanced Users, which can only be changed by editing nbMaxFindHistoryFind and similar attributes, as described in the User Manual. When manually editing config.xml, you have to follow the steps in the Editing Config Files section, reading about the differences in how you have to treat config.xml because of its unique status in Notepad++'s inner workings.