So, if it can read an APFS volume, doesn't that mean it can easily upgrade to Mojave or Catalina, which will be able to format or be installed onto an APFs volume?
The ability to READ an APFS volume will have no effect one way or the other in upgrading to Mojave or Catalina. You could just as well remain in Sierra. Remember that we are roughly six months away from MacOS 10.16 (the successor to Catalina) so putting off going to Catalina would mean your learning curve will just get higher and steeper the longer you hesitate.
MacBook Pro - M2, Ventura 13.6 Safari Tech Prev 17.0 Safari 16.6 Firefox 116.0.2 iPhone 7 Version 15.8
