Running Catalina and Mojave via same user folder

[Beliblis]

Hi,

I've been running Mojave for a few years now, and just installed Mac OS Catalina on an external hard drive, currently using the very same user folder as Mojave. Trying to find out about software compatibility and work with Sidecar a bit, before I make the full transition to Catalina and possibly BigSur.
Are there any caveats / things I need to be careful with when sharing one user folder under 2 different operating systems?

My setup:
Internal MacMini HD: Mac OS Mojave
External 256gb SSD: Mac OS Catalina
External 512gb SSD: User Folder

I'm not going to use Apple Mail whilst in Catalina (because this would mean updating the mail library, which would mean it won't work under Mojave anymore). IMAP mail on iPhone/iPad does the job for now, whilst I'm in Catalina...

So, Apple Mail: sorted
Desktop / Downloads / Pictures folders etc: 100% "data" anyway, so I can't see any problems there.

How about other software (and licenses)? Photoshop/InDesign, Cinema 4d, Keynote, Contacts, DaVinci Resolve etc...
Can I boot in Catalina, work with any of those apps, then reboot in Mojave, and carry on working with those apps?

Thank you!!

 

[velocityg4]

I'd think there'd be too many problems actually sharing a user folder between two OS versions. I never tried it but the big problem to me would be the Library folder.

Why not just have different folders. Then just shortcut to the same Documents, Pictures, Video, Music, &c folders. As those shouldn't be a problem.

Other issues may be Photos. As the Photos database may not like two different versions accessing it.

Then there's iTunes. I can't imagine iTunes and the separated media apps will play nice with eachother in the same Music folder.

 

[saudor]

Third party apps (including hacked iTunes on Catalina) will work fine as the directory structure will be fine.

the OS specific library data will not though. (E.g iMessage and even spotlight) macOS will continuously reindex your drive when you reboot to each side

 

[Beliblis]

I'd think there'd be too many problems actually sharing a user folder between two OS versions. I never tried it but the big problem to me would be the Library folder.

Why not just have different folders. Then just shortcut to the same Documents, Pictures, Video, Music, &c folders. As those shouldn't be a problem.

Other issues may be Photos. As the Photos database may not like two different versions accessing it.

Then there's iTunes. I can't imagine iTunes and the separated media apps will play nice with eachother in the same Music folder.

Photos is not an issue, as I don't really use it.

Contacts, however, has been a problem (even though I didn't open the app in Catalina):
I'm using iCloud to sync, and all my contacts are still there on my devices. But after first boot into Catalina, all contacts were then gone when I booted into Mojave.

Might revert to your shortcut solution. (Although, to be honest, I enjoy being able to access the "other" OS's desktop folder. The moment I have two "proper" different user folders, I won't be able to cross-access them I guess).