Hi Pauly.6.String and welcome to the forums.
Pauly.6.String wrote:Hello. I had Sampletank 3 working after I updated to macOS Catalina. I just re installed the OS to find its not compatible. Cant install it but is there a way to restore it from a Time Machine backup?
This is sometimes an issue when reinstalling an OS on a Mac. As ST3 was already in place, the OS update (I guess "over the top") just disregarded the apps already installed. When it comes to a clean install, the OS might not like an older installer and not work - as you've seen. Catalina in particular no longer runs 32-bit apps, which I suspect the installer might have been.
I don't think a TM backup will help in this instance either, possibly only a clone using something like SuperDuper or CCC would do what you want. However.....
Do the sound content installers for ST3 work? Is it just the main application that won't install/work?
If that is the case, you can use the free version of SampleTank 4 Custom Shop that is in your User Area to use your old ST3 sounds. Install the ST3 sound content, then install ST4CS and in Settings>Sound Content add a new pathway to where the ST3 content is and it will be added to ST4 sound library.
If the ST3 content won't install, it might be an idea to open a ticket with Official Support as they may have specific guidance on how to do this
https://www.ikmultimedia.com/contact-support/sw/Hope that helps. Let us know how you get on.