This doesn’t help with your observation field ask (although if this feature request was implemented, you could use the same trick), but I discuss a workaround for the AND logic for annotations in this tutorial here:
https://forum.inaturalist.org/t/searching-for-annotations-basic-to-advanced/65375
It’s definitely not as good or useful as built in functionality would be, but it can at least get you part of the way there.