Not able to change network settings on Kubuntu 20.10

Solution 1:

In order to completely remove all previous network settings, open a terminal and do:

sudo rm -r /etc/NetworkMananager/system-connections/*

Restart Network Manager:

sudo service NetworkManager restart

You should be all set.

EDIT: Your interfaces file doesn't appear to be correct. Please change it to read:

source-directory /etc/network/interfaces.d

Reboot and tell us if there is any improvement.