It seems like this . . . behavior no longer applies. I’m not 100% sure why, but it could partly be that iOS/iPadOS does not use ram as a cache for external drives. Maybe it just writes through or flushes very quickly and frequently. This would drastically lower (potential) write performance but maybe that is the trade-off the have made.
For Apps that are writing to such, maybe they have to use an API (instead of typical OS block writes) to handle such disruption before a full write is completed. A journaled filesystem is clearly not a requirement.
Maybe they are just accepting less guaranties around such data. After all, these are not system executables or anything like that. I have seen no white paper on this (yet).
My drive was constantly spinning and the read indicator was flashing. I tried to close the app and wait for 30 minutes but it still went on. So it must've been doing something... I just decided to pull it out for now, but I don't think it's a good idea though.
All external disk writes are synchronous on iOS. You can pull tie drive whenever you want without (non-beta related) filesystem access. Of course that doesn't mean whatever was writing to it was actually finished.