In this thread with a similar MacBook Air from 2011 and the same network card on Zorin 17 Lite the brcmsmac driver seem have to worked on kernel 6.8 (the thread is very long and mainly about the nvidia drivers).
I'm not sure if that would be an idea if the other solutions don't work. Look at the posts 10-14.
You can also take a look at that Linux Mint thread. The user there had also more success with LM 21, which is similar to Zorin 17 (ubuntu 22 based, kernel 6.8).
https://forums.linuxmint.com/viewtopic.php?t=451899
He had linked an ubuntu bug thread where the recommendation was given for problems with the broadcom sta driver to set the kernel parameter iommu=off (add it with root rights to the file /etc/linux/default and then update grub sudo update-grub and reboot). I'm not sure if it can help you, but it may be worth a try. If it doesn't help, remove the added kernel parameter, update grub again and reboot.
To open the file with root rights:
gnome-text-editor admin:///etc/default/grub
That is the line in the grub file. It should look like this:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash intel_iommu =off"
And when you have opened the file, it is the best also to change two other lines to
GRUB_TIMEOUT_STYLE=menu
GRUB_TIMEOUT=10
to display the grub menu with the advanced options when booting.
If you don't use thunderbolt or hot plugging and you are the only user of the system, the security risk should not be too big to test it if you want to stay with Zorin 18.
I really don't want to talk you into using an older system if that's not what you want. From my own experience with my older Dell laptop from 2012, I can only tell you that I was using Linux Mint 22 XFCE and switched back to Zorin 17 Lite because I ran into problems with my fans after updates (on Zorin 17 Core my fans were loud, too). It runs much better. I'm going to make the most of this year while there's still support for Zorin 17 (until Jun 2027).
You can also test on Zorin 18 if the kernel 6.8 helps. You can install it on Zorin 18, reboot and then at advanced options for Zorin select kernel 6.8 to boot from.
sudo apt install linux-headers-6.8.0-136-generic linux-image-6.8.0-136-generic linux-modules-6.8.0-136-generic linux-modules-extra-6.8.0-136-generic