Recording to a ring buffer and a way to dump to external storage would be handy and I’ve thought about it often. It also turns out that storage is very cheap so if you don’t mind some work every now and again you can just record constantly to a larger piece of storage.
I’m not sure if all the zoom recorders do this but the H6 (and I think H5) can mark spots in audio files that get recorded (it’s a text file in the same directory). Put a 128Gb card in and you have about 400 hours of storage. It won’t let the files go over 4Gb each (iirc) meaning you’d have multiple files rather than one (inconveniently large) 128Gb one.
Assuming it records 24/7 that’s over 2 weeks of audio, so once every 2 weeks (if it’s recording a mere 4 hours a day you have 3 months worth) you have to clear the card and save anything you marked. This isn’t ideal, but as it’s quite infrequent it’s not too bad. You could also likely script it meaning no real “thought”, just plug it in, have it grab your snippets, then clear.