If you make your living as an editor using Premiere Pro you will eventually run into the issue of needing to open a project in an earlier version of Premiere, and Adobe does not want you to be able to do this. This is insanity, especially for anyone who comes from the AVID side of things, but at least there is something you can try.
ELEMENTS, a German Editing workflow specialist company has put up an online tool for downgrading your Premiere Pro Projects, check it out here. Obviously make a copy of your project file before you try it.
I know Adobe now lets you open current projects in beta at least and go back and forth, but there really should be some way to save as a previous version if necessary. And I know they don’t want you to since they only support the 2 most recent versions, but honestly who doesn’t know places that stick on earlier versions. The lead editor at the place I am working at now insists on staying with 2019 currently.