Where to find a list of residential numbers?

I'm not sure if there's anyway to get a phone number for a person online anymore (since the end of 2020) as they've stopped publishing them.

Also if a person chooses to not have their number "Published" (like in that it wouldn't appear in the phone book at the time), it also wouldn't be available to Directory Enquires either

You're best bet may be social media or do you have their address, writing to them may be the only option.

These days the likes of Facebook is about the best option, they might not have an account but some mutual friend/relative might and most communities now have their own Facebook page so someone should know them.

If enquiries don't have it, the number isn't listed so wouldn't have been in the printed phonebooks either. Any library will have a recent set, but they are not printed anymore.

Well, you're not going to find it then. People who aren't online (or are very private online) are now much less contactable than they were 20 years ago.