Hi,
You mentioned an iP9900. Could it posssibly be a Canon i9900?
https://www.usa.canon.com/internet/portal/us/home/support/details/printers/support-inkjet-printer/i-series/i9900?tab=drivers_downloads
If so, there are supported drivers for Mac OS X 10.6 Snow Leopard (and 10.5 Leopard) only. These are probably far too old to be used with a modern Mac, but you could of course try a download anyway. As with any experiment, there is a certain risk. Software and hardware problems cannot be ruled out. Data may be lost. So, do not proceed unless you know what you are doing. Make sure that you have at least three backup copies of all important files (documents, photos, et cetera).
Yes, be careful with downloads from the Internet. There are a number of third-party sites using (parts of) a printer manufacturer's name in their web addresses. Download from an official Canon site only, or from another trustworthy source (such as Apple).
If you have access to an older Mac that can run Mac OS X 10.6 Snow Leopard (or possibly some of the following operating system versions), you could perhaps try to connect the printer to that computer and print from there. If necessary, transfer files from the Big Sur Mac. You may also want to check what happens if you let the old Mac share the USB printer on the network.
Share your printer on Mac - Apple Support