Is there any way to open / migrate to an earlier version?
Which edition do you have ?
If Substance edition from substance3d.com you can in My Licenses section download the version you which.
If Steam edition, then you can download the previous version.
If a version launched from CCD, then click on the ldots like :
I'm using 6.2.1.
What do you have in the about window ?
If nothing brackets you launch from CCD, so you have one of the 3D offfers, texturing or collection editions.
If you have Substance Edition, then you have Substance Edition.
If you have Steam Edition, you launch from Steam and you have Steam edition.
Not sure which version was used, I am sure though it was using Adobe services. The version I have I think was before Adobe took over.
Sorry I'm looking to open a Project on an older version not the app itself.
This is not possible once you project saved with a newer version, it is most likely that you wont be able to open it with the previous version.