MacOS: Unable delete saved wifi networks

After several more hours of active use on Mac and phone, no old networks have reappeared.

Let's go back to basics, if we may. I know when I get too familiar with my Mac I miss steps. There seem to be two steps that are missable:

• In System Preferences> Network> Advanced, after using the '-' sign to delete a network, there is on OK to press. Worth doing even if it genuinely has no effect
• In System Preferences> Network after pressing OK, above, if you have made changes, the APPLY button is no longer greyed out. That needs to be pressed.

I have no idea if this is a real solution, or just my Mac and phone combination not (yet) showing these symptoms you describe, or whether you have done all of these steps yourself. Since the issue has been around a while its unlikely that I have stumbled on the solution where no-one else has! Still worth double checking, though.