This morning I also encountered problems with my Canon PIXMA 7720 printer due to my using Mojave 10.14.3. However, thankfully, I did find a newer print driver, newer scanner driver and newer Canon Utilities apps on Canon's website. As a result, my printer is back to working again. It's a real bummer when we suddenly discover that our printers are no longer compatible with macOS. That is exactly what happened with my previous Canon printer, and I didn't even have it that long when it fell by the wayside. But, that's life, and there's really not much that we can do about it, except bite the bullet and move on.