I’ve finally got my satisfying solution: In this video, @tallguyjenks mentions and links this video, in which this Siri shortcut is linked and explained. For my part, I actually didn’t follow that link at first but searched for the video myself and found an earlier one with a different shortcut link. The idea is really the same in both cases, but I find the later mentioned video to be more instructive, somewhat easier to follow. Plus, this older shortcut doesn’t depend on third-party software. iOS 14 suffices on its own. I found the shortcut has even been referred to on the forum before.
Anyways, I adapted the shortcut to my idiosyncracies (including my YAML setup and whatnot) and now have just what I need. Well no, it’s even simpler than what I (could have possibly) hoped for. Tap the phone on the back, enter text, done! It’s worth a look for anyone remotely interested in making quick capturing efficient and convenient.