I run into the same issue and ended anti-aliasing my files by hand which took way too long… so I did what developers do best: automated the process!
I hope UE will eventually fix the issue, but in the meantime, you can use this web app to AA your files and even RGB pack them into a single texture file.
https://umg-antialiser.pages.dev/
No network calls, no trackers, no nothing, everything runs in your browser, your images don’t leave your machine. Source code also available on GitHub (see link at the bottom of the page).
