Well, root definitely works (tried with Call Recorder).
You can simply uninstall the Magisk Manager, grab whichever you want (stable, canary) and then patch the latest boot.img. Just like now. Nothing tricky honestly. Once you update to a new system version, your boot.img will return to stock/unrooted anyway.
Though, Canary is like... super-alpha. It's supposed to be bleeding-edge, the freshest. So it's weird Canary failed, while Alpha works fine.
I updated via OTA. I don't think OnePlus provides flashable ZIPs at all. To do a Pixel like, full fastboot "-w" wipe update. You could upgrade and then wipe. But other than that...