Keep two versions of macOS
Q How to keep Ventura available on my M2 MacBook Pro when I upgrade it to Sonoma?
AThe best solution depends on what you still want to be able to do in Ventura. If you want to run App Store apps, access iCloud or do anything else dependent on your Apple ID, then the only way to keep access to an older version of macOS is to install it on your Mac’s internal or an external drive. If you don’t need those, then it’s quicker and simpler to run Ventura in a virtual machine (VM).
Dual-booting between different macOS can prove fiddly to set up, and some find it unreliable. While you could install both on your Mac’s internal SSD, if anything goes wrong it could put your primary Sonoma system at risk. Running Ventura from a bootable external SSD is safer, but requires assignment of ‘ownership’ to that disk for it to become bootable. That’s detailed at bit.ly/mac395venturaboot.
If you can live with the limits imposed in a VM situation, you could use Parallels Desktop, UTM or my own free Viable from bit. ly/mac395viable. Performance is near-native, you don’t have to restart into Ventura to use it, and it’s really convenient.