Any recommendation for an iOs app you like that will loop a portion of a song?
Before posting here I googled and learned you can sometimes do it in YouTube if clipping is enabled. This seems to be limited to one minute. Also a guy has a web page that lets you enter a YouTube ID and loop a segment of the video from his site: https://www.looptube.xyz/
For looping videos I use FiveLoop app - it is built for guitarist wanting to practice using videos. So it support slowing down as well. Looping can even be controlled using a midi footpedal (I do not use this feature though)