Hi,
>I've run every "fix" recommended online concerning Canon
Have you tried a full power-cycle sequence (including the router, in this order, with these waiting times)?
Power off the Wi-Fi router, the Canon printer, the iPhone, the Mac, and all other devices/computers. Wait two to three minutes. Power on the router. Wait two to three minutes. Power on the Canon printer. Wait a minute or two. Power on the iPhone and the Mac. Finally, power on all other devices/computers.
Are you using VPN on the iPhone?
See, for example, a reply by Lawrence Finch in Stuck on gathering printer supplies infor… - Apple Community.
Have you checked whether the printer has been updated to the latest firmware version?
https://www.usa.canon.com/support/p/pixma-ts9520
Is the printer wirelessly connected to the Wi-Fi router? If so, just as a test, any change if you wire the printer by Ethernet to one of the LAN ports of the router instead? AirPrint works with wireless (Wi-Fi) or wired (Ethernet) network connections. The Mac (and the iPhone) can still be wirelessly connected to the router.
If nothing else works, you could perhaps try the Canon PRINT iOS app as a temporary solution.
https://apps.apple.com/us/app/canon-print/id664425773
EDIT: Just noticed that Lawrence Finch had posted a reply while I was composing my message, so I have without intention more or less repeated some of the things already suggested.