Hey there! thanks for trying out the theme <3
However I'm sorry about the UI Scaling, I don't have any fix for that, at least not for now ): I made the theme using 1080p at 100% and therefore it works perfectly in 4K at 200%, the problem is that it ends up looking weird at 1440p because ideally we would need a 150% scaling for that but Aseprite doesn't have it.
Since it's not the first time someone has asked me for a 1440p solution, I've been thinking about making a variant specifically made for 1440p, but I can't give you a specific day for that release, hopefully I'll be able to get it soon! So please check the project page again in a few weeks, I'll be posting a new Dev Log once it's released (: