I just 301 redirect all of those from other sites to a custom 404 page.
Of course if its one I caused, usually an internal link typo I fix it.
You can chase them down until you pass out but there will always be more.
Don’t say they’re fixed it they’re really not.
Let me add that I used to do it in my htaccess file but found out that I could just enter the custom 404 page in my host account. It works just like the bounce back url feature RA offers.