@RobinBetts Hey, sure, I've just awarded the bounty, so you can go ahead and mark this as duplicate and close it ;)

Thanks a lot for the tip. The normalize node does work for black and white images. The reason I cranked up the emission strength to 100 is that a strength of 1 didn't appear white enough. Figured out that this is due to the Filmic (or the new AgX) view transform (see Color Management). For this project, I've now set it to sRGB where an emission strength of 1.0 corresponds to "full white" (#ffffff). Now, the anti-aliasing is working as expected even without any anti-aliasing node in the compositor ;)

@Crantisz Thanks a lot for the link, that solved my problem ✅

Thanks, this is exactly what I was looking for. Feels better than having to do Alt + B