CD/DVD external drive for M1 Mac?

Yes. The apple Super Drive drive can work on an M1 Mac using an appropriate adapter, or in some cases through a powered USB hub. However many USB hubs have been shown to be problematic for this, and as such a direct connection using an adapter is recommended. Click here ➜ How to connect the Apple USB SuperDrive - Apple Support

and to add to Phil0124's reply, I have seen more than once where a third party USB-C to USB Adapter didn't work. but in those cases, they tried the apple branded USB-C to USB Adapter which then allowed the superdrive to work.