PostgreSQL uninstaller doesn't require any internet connection to uninstall the software
So I suspect the error is somewhere else. Can you please share the uninstaller log file can be found inside C:\Users\$USERNAME\AppData\Local\Temp\uninstall-postgresql.log
During the uninstallation of 10.20 , our organization only allows administrators to install and uninstall the software, and blocks admins from communicating with the internet. We have a closed network with no internet access that the software uninstalls from just fine. Our semi open network has internet access but administrators are unable to uninstall the product due to no not being allowed to communicate with the internet even though the connection exists.