Quit and Open Safari Extensions Preferences Dialog Not Working

I did a clean install of Big Sur (11.2.3 on a 2018 MacBook Pro). I began installing extensions in Safari as I resolved to move away from Chrome. 1Password, Evernote, Grammarly, and Honey installed seamlessly. **None required the Quit and Open Safari Extensions Preferences until I attempted to install the venerable One Tab Extension, then the Nimble Prospector extension, and finally the Blue Canoe Pronunciation Dictionary extension.

After installation of each, and clicking Open in the App store, a dialog box opened with "Quit and Open Safari Extensions Preferences" on a button. When I click the button, nothing happens. The dialog stays on the screen. The extension does not appear in the Extension Preferences pane (not even after I click to another preference pane and back again).

I've made sure to leave UNchecked the Prevent cross-site tracking, and Block All Cookies preferences.

I've cleared the history. I've booted into Safe Boot just in case things like my Intego Virus Barrier software might have been interfering. Same results.

I've reinstalled Big Sur (twice) to try to reinstall and hopefully reset Safari.

I've given the extensions (apps) Full Disk Access in Security.

I've tried this on my daughter's M1 MacBook Air, and it worked exactly as it should, meaning the extensions installed successfully. Is there a setting or a preference file somewhere that I need to nuke to help reset this weird obstacle in my system?

I really appreciate any help. Thank you.