Can I Keep an older version of Photoshop

If you look at the available Previous Versions list, you'll see a big gap between 22.2 and the next more recent version.  This is obviously to give people the option of using Photoshop 3D as others have said.  So we know Adobe are supporting 3D as much as they feel able, but you can be sure that won't last.  For instance, we have recently learned that Adobe will no longer support reactivation of CS6, so if your drive breaks, or computer spontanioualy combusts, you can no longer use the software you paid for.  I'm actually a bit surprised that Adobe are being so kind regards V22.2 because I'm sure they'd rather their customers paid for the Substance apps.

Photoshop 22.2 does have the distinction of being the last version that has fully

working 3D, so that's why it's still available for download/install from Adobe, however, for

how long nobody other than Adobe knows.

You can have more than one Photoshop version installed.

You can keep using Photoshop 22.2 as long as you like,, but if later you upgrade to a new OS, it might be incompatible.