This might actually be incorrect. I decided to use my Boosteroid account to start my game over and not only is my EA save still in there, there are migration instructions if you want to keep your EA save going. I actually didn't because I wanted to start over on the real build anyway, but just FYI. I'm assuming once the full Mac version comes out next month, I can just resume my save without Boosteroid sitting in the middle, meaning I can up the resolution higher than Boosteroid is allowing.
As a general thought on Boosteroid, it's still very much in beta, and I am still incredibly impressed with it. Elden Ring is still a buggy mess on Windows, and I have a lot of issues with it crashing when I first load up my saves, but that's not Boosteroid's fault. I don't have the same issues with any other games in my library.