My Apple Superdrive stopped burning CD-Rs on 11.2.3. I have ordered a new drive, but could it be the OS?

you're welcome. and after replying earlier, i think you might want to try these steps:

Reset NVRAM or PRAM on your Mac - Apple Support

How to reset the SMC of your Mac - Apple Support

they might not help, but it wouldn't hurt to try. :)

i don't think it's a big sur issue. i'm still using my apple superdrive with my 2019 iMac on 11.2.3. i successfully burned an audio CD a few days ago. before replacing the drive, if you know someone else with a mac, maybe try and see if the drive works with it. you could also try unhooking the drive, then restart the mac, reconnect the drive and try again. and you can also try a different blank disc to eliminate a faulty disc as the source of the problem. if all else fails, it may be time to replace the drive. you could get another superdrive or you could shop at OWC to see the other options you have.