If you delete a Wi-Fi network profile in macOS, your Mac will never connect to this hotspot unless you do it manually by selecting the network and typing its password (a.k.a. network security key). Here is how to disable auto-join and forget a Wi-Fi network by deleting its profile in macOS Big Sur.
How to Forget a Wi-Fi Network in macOS 11 Big Sur
Be advised that if you remove the profile of a certain hotspot, all your other Apple devices such as iPhone, iPad, iMacs, etc will also “forget” this network. If this is not what you want and you wish only your Mac to stop auto-connecting to your Wi-Fi, scroll down and read about disabling the Auto-Join option.
Open the “System Preferences”:
Go to the “Network” section:
You can do the same by clicking on the Wi-Fi icon in the status menu in the top bar and selecting the corresponding menu item:
Make sure you have “Wi-Fi” selected in the left pane and click the “Advanced…” button:
Select the Wi-Fi network the profile of which you want to delete
Click the “-” icon:
Confirm by clicking “Remove”
Now click “Apply”. However if you don’t click “Apply” but close the window and even opt to not save settings, the Wi-Fi network profile has been already removed.
Video Guide: How to Forget a Wi-Fi Network on macOS Big Sur
Disable Auto-Join Instead of Removing Wi-Fi Network Profile
Note, that if you wish to only prevent your Mac from automatically connecting to the certain Wi-Fi network when it is in the range, you may want to just disable Auto-Join. All you need to do is just unset the “Auto-Join” checkbox.
The difference is the following: if you untick the Auto-Join, you won’t need to re-enter the password (security key) in case if you decide to connect your Mac (or your other Apple devices using the same iCloud account) to this hotspot.
Which Option to Choose?
If talk about a saved profile of a public and unprotected Wi-Fi hotspot, delete it to make all your devices to “forget” it. If it’s about the network of your wireless router — turn off the Auto-join on your Mac so that your iPhone & iPad will be able to auto-connect to it as usual.