If your vault is sync via iCloud, and you aren’t looking to open the note after it is appended, the ios internal commands are also great. I don’t use any other apps/tools such as the URI command, ios’s internal commands have one that allow you to prepend/append files in the icloud drive. In obsidian’s case, since all notes are just markdown, I can easily select any one file.
I set some formatting that help wraps around what I input in the prompt, so the inbox items are organized in a minimal way.
here is the shortcut in case anyone might find it helpful: shortcut: quick thought/laters into one note
Unlike most people here, I prefer to have everything inbox-ish in one note. Everything else in my vault are “processed”, but inbox isn’t.