Canon mx850 on catalina 10.15.7 - driver

Another thought... that printer was obviously working with some device in the past, so you can still keep using it with your Mac — if that device supports Printer Sharing.

For Macs, that would be Share your printer on Mac - Apple Support.

Excerpt:

"You can share your printer with another Mac or with a UNIX computer."

Open source Un*x drivers are available that can support printers as old as Unix itself — which dates back to the dawn of computing.

Even a tired old Mac would make for a rather expensive print server, but a print server running Un*x can be implemented for a few dollars. Your Canon is nearly certainly to work that way, and it could even do it wirelessly.

When you eventually decide to get a newer Mac, you won't have to change a thing about the print server. Since the printer communicates directly with the print server, a new Mac will be able print to that printer. It will work with macOS "Tahoe". It will even work with an iPhone.

For Windows PCs: Use your Mac to print to a printer connected to a Windows computer - Apple Support. Legacy Windows PCs are often found abandoned by the side of the road, where they belong.

Yes... but it depends how much time, effort, and money you wish to expend toward keeping that printer in service. Briefly stated you would need to invest in a print server.

The good news is that a print server wouldn't cost much money. The bad news is that you can probably purchase a new printer for about as much as a print server would cost.

More bad news, new consumer-grade printers aren't nearly as good as the older ones were. They are literally designed to be disposable. Once the ink runs out it's best to just throw them away and buy a new one. Somehow, that's supposed to be better for us.

About AirPrint - Apple Support used to include a list of AirPrint-compatible print servers that would work, but Apple dumbed down that webpage and now I wouldn't know how to begin looking for one.

Not wanting to leave you with nothing but bad news, I am working on a User Tip that will describe a method by which old / legacy / orphaned printers can be kept in service.

As you are probably aware, Canon's "PIXMA MX850 has been retired. Product support is no longer available. Driver and content updates are not being made."

Should you ultimately decide to retire that old but otherwise perfectly serviceable printer, I recommend reviewing MrHoffman's User Tip Which Printer Should I Buy? - Apple Community.