What I guess, here within this thread, is that you are probably using another laptop (another PureOS based installation on another Macbook) and therefore people here need to know which WiFi chipset is inside your current device:
sudo lspci | grep -i wireless
And hope that solution to working WiFi on this device is just around corner, as it is for sure. But first, please remove: deb http://deb.debian.org/debian buster non-free line from this Macbook sources.list file.
As second, please download: http://ftp.de.debian.org/debian/pool/main/d/debian-ports-archive-keyring/debian-ports-archive-keyring_2020.02.02_all.deb package to some particular folder and install it from there:
sudo apt purge debian-ports-archive-keyring
sudo apt update
sudo apt upgrade
sudo apt autoremove
sudo dpkg -i debian-ports-archive-keyring_2020.02.02_all.deb
As next, please read carefully this Debian instruction and download: http://ftp.de.debian.org/debian/pool/main/i/isenkram/isenkram-cli_0.48_all.deb in order to (please be aware that this particular package includes few dependencies, yet automated install isn’t excluded for now, we don’t expect problem there):
sudo dpkg -i isenkram-cli
sudo isenkram-autoinstall-firmware
Please post isenkram-autoinstall-firmware output here, please share it with us. As related to above link, latest non-free firmware collection is, as well (You don’t need to use them), here: https://cdimage.debian.org/cdimage/unofficial/non-free/firmware/bullseye/20211009/. Working with above tips should be easy for you (even if I forgot something important), therefore please let us know how this newly added non-free functionality from Debian 11 Team worked for you.