Problems from inherited software from old macOS versions

I have a MacBook Pro that has inherited material through Migration Assistant since Mac OS 10.0 Cheetah at least, and maybe earlier. Several OS operations do not work properly on the admin account which has that inheritance, but work fine on a new standard account. Examples are:

• FInder Add to Photos extension (and maybe other extensions) where nothing happens.
• application windows do not stay on external monitor over machine sleep and revert to the built-in screen.

Help appreciated in either finding the offending file(s) that have been copied from an old Mac OS that stop correct operation, or in defining a process to rebuild the user account correctly. I am reluctant to mass delete files and re-install as I don't want to lose years of preferences. The problems have continued over several recent system updates, major and minor.

Machine: MacBook Pro Nov 2023 with M3.

OS: Sequoia 15.7.2