I don't think I've seen this mentioned anywhere, but on my iPad pro at least, playing audio with two-finger double-tap or the play headphone button is now a stack, and I'm reasonably sure it wasn't before iOS 18.
Example, I'm listening to a book inSpeech Central, pause it, and go into youTube to watch a video. Do that for a bit and go out and hit play, and I'm back reading my book.
It even seems to work three layers down, start reading an audio book in book player, pause it, start reading another in speech central, pause that, go into YouTube. play something for a bit and leave, and you're in Speech Central. Stop reading the book in there by exiting the book and you're in Book Player.
I *think* it's even stopped playing Apple Music by default if it's got nothing better to play, which I have to say will make my life a lot less startling if it's true, ☺️.
Now I have no idea exactly how well this might work on older devices with less memory, since I imagine it wouldn't work if the app that was playing got swapped out, although I don't know this for sure. I also don't know how many levels this could theoretically go for. I did find it interesting, though.