I have not heard anything of Adobe’s plans, but I would not worry, I am sure they will support Metal on Mac OS. They will have done most of the work for iOS, not only in supporting Metal but in porting from Open GL to Metal. So 90% or more of the code needed will be the same.
There is no urgency as Apple have only announced the deprecation of Open GL. That is a warning that it will probably be removed from the OS one day, but that day could be long off.
Hypothetically the earliest it could happen is Mac OS 10.15, but that is not even announced and will not appear for 9 months or more. And I would not expect it then. I think it will be more like 32-bit apps, and take place over a number of OS versions, so over a number of years.