This question has materialized after this strange interaction: multiple instances of macOS, installed on different hard drives on the same machine, share settings.
Example: I have this MBR 16”, 2020. On the internal hard drive I was running Catalina. Let’s call that (A). On an external SSD I had installed another copy of Catalina. We will call this (B).
While using (B), When adding folders in the “do not search” setting for Spotlight, whatever folders I would add would be added in the “do not search” list of (A).
When connecting to a certain WiFi only on (B), the WiFi info was added to (A) as well, including password.
Unless unmounting the internal drive or encrypting both of them, they would communicate for some reason when you would expect two separate entities of macOS on two different drives to not share configuration files.
Why does this happen?
LE: Corrected Spotify into Spotlight