Since the Channels app doesn't support iOS' native Picture in Picture, I'd been using the Channels Web UI to allow that feature, when I've needed it. I've recently discovered an easier method for live TV watching on my iPad via Channels DVR though, a solution which specifically incorporates PiP.
Rather than navigating Safari, or a bunch of bookmarks, which requires lots of navigation and taps, just to channel surf or set up a PiP window, I'm now using this app instead: https://www.tvstreamsapp.com/
I added the .m3u8 URLs for all of my favorite channels, which I got from the Channels Web UI.
The TV Streams app has versions for iOS, MacOS, and tvOS, and the channel bookmarks you add or edit sync across all platforms via iCloud. The basic version is free (ad-supported) and the Premium version is $8. A one-time purchase enables Premium on all platforms.