You could install SAMBA on your Debian image, and whatever folders you share with SAMBA will be accesable via network locations in your Mac's finder. If you wish to go that route, here are instructions on setting up SAMBA in Debian Buster: https://linuxconfig.org/how-to-set-up-a-samba-server-on-debian-10-buster.
Or you can set up a file sharing on your Mac to share a folder that can be accessed by Debian. If you wish to go that route, here are instructions on sharing folders on your Big Sur: https://support.apple.com/guide/mac-help/set-up-file-sharing-on-mac-mh17131/mac