Hi,
Yes, the drivers for the MX870 on Canon's support site appear to be for OS X 10.11 El Capitan and
earlier. You may want to try them with macOS 12 Monterey anyway
Alternatively, you could perhaps try the Canon Printer Drivers v3.4 for macOS download from Apple (despite the System Requirements). A Canon MX870 series version 16.10.0.0 driver is mentioned in Printer and scanner drivers for Mac - Apple Support. This may not work at all. Look upon it as an experiment.
It has often been suggested to check whether Gutenprint drivers will work with macOS Monterey and older Canon printers (MX870 drivers are listed on the Gutenprint site, but as experimental). However, normally, it is recommended to download from the printer manufacturer or from Apple only.
Sometimes, an old printer driver may in fact be compatible with the latest operating system version, but the installer does not allow it (perhaps because of an old certificate, or something similar). There may be ways around this, but they are not supported...
If necessary, reset the printing system between tests.
Reset the printing system on your Mac to solve a problem – Apple Support (UK)
Add a printer to your printer list so you can use it on Mac – Apple Support (UK)
As always, before testing anything, make sure that you have multiple backup copies of all important files (documents, photos, et cetera). Software conflicts can never be ruled out.