Note: I do have a beefy windows machine at home that can do 4.21 just fine, but I'm away for another two months, so I won't be able to use it. I was hoping to get some cool prototypes in before I got back.
Hey, thank you first of all. I sadly have really bad news for you. I tried a numberos ways to downgrade the project but all of them fail -> map cant be loaded+ no blueprints as well :( .
Once I kept all developed versions but due to people downloading every version (even when simply worse) + unnessary cluttered I delted them.
I sadly didnt know that there may be 3rd party tools that require a older version. Now to the "better" part: I have still kept one of the earliest versions around. It is a really bare bones. The character blueprint is messy, some features are missing and in general it is just worse, like you would expect. I will set it to public so you can download it again and maybe try it out? Just be aware that at home you will have a way better experience in 1.7 https://kai20.itch.io/exploration-kit/devlog/56534/17-release-i-would-almost-cal...
I am sorry I could only half resolve your problem but for the future I plan to keep a backlog even though actually supporting it with updates might get messy