Did you test to set 5 GHz band for Wlan if your computer and router support it?
Sometimes the advice is given to add
options iwlwifi bt_coex_active=1 to /etc/modprobe.d/iwlwifi.conf
but I also read posts where the opposite
options iwlwifi bt_coex_active=0
helped when a intel sound card is used and there are interferences between wlan and bluetooth.
I'm not sure which one is better to try. But you could test both one after another and when it doesn't help remove the added line from the file.
I'm not so familar with the given command there and I'm not sure if it is the right one for Zorin 18, because it deleted the content of the existing file and I think you should only add the line at the end of the file.
Maybe someone else can give you better advice.
Edit: When you use this command it should add the line to the existing file and not overwrite the content:
echo "options iwlwifi bt_coex_active=1" | sudo tee -a /etc/modprobe.d/iwlwifi.conf