Hi,
If it is not possible to return the printer, you would have to look for some kind of workaround.
You could try to save to PDF or JPEG on the Mac, then (somehow) transfer to an iPhone or iPad, and finally print from there (via the Canon PRINT Inkjet/SELPHY app). Not ideal.
Since there are Windows drivers for the GM2040, another option could perhaps be to try a virtual machine (running an appropriate version of Windows) on the Mac under Big Sur.
The experimentally inclined may even want to test a number of printer drivers for other Canon printers (the G2000 series CUPS Printer Driver would be just one example of many). However, this will take time, and there is absolutely no guarantee for success. Also, there is a certain risk involved with any printer driver experiment. Software/hardware problems cannot be ruled out. One may have to erase and reinstall everything on the computer. Data may be lost. So, do not proceed unless you know what you are doing. Make sure that at least three backup copies (on separate media) of important files (photos, etc.) are available before doing anything. Also, ensure that printer driver downloads are from official Canon sites (not from third-party web sites using similar names), or from Apple.