I am currently using the Photograhy Plan apps (PS, LR Classic and Bridge) on my 2019 iMac using OS Mojave. I have an external drive connected to the iMac and I have installed Mac OS upgrade Big Sur on it. This is in order not to ovewrite Mojave if I discover comptibility problems with Big Sur. If I do have problems I can always change the startup disc back to Mojave. If all is well I will repeat this procedure with the most recent Mac OS, Monterey. My question is : how do I install a new copy of my Adobe apps on to the connected external SSD drive for this procedure? It is my intention to eventually remove the copies on the external drive when I finally overwrite mojave with the most recent Mac OS.
As you are isolating one of the operating systems and testing the second on a different drive, you can reinstall the apps once you are booted on the newer operating system, which will by default target the external drive on which you have the operating system configured. You can keep the Adobe Apps installed on Mojave and then boot from the BigSur as boot drive and install the Adobe apps there again.