Disable systemd-resolved on ubuntu:
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systemd-resolved is apart of systemd and is a replacement for /etc/resolv.conf for ubuntu dns search.
I disable this since It causes many slowdowns.
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To disable I do this:

Disable and stop the systemd-resolved service:
sudo systemctl disable systemd-resolved
sudo systemctl stop systemd-resolved

Then put the following line in the [main] section of your /etc/NetworkManager/NetworkManager.conf:
dns=default

Delete the symlink /etc/resolv.conf
rm /etc/resolv.conf
(This will restore the old /etc/resolv.conf that is not a system link but ubuntu used to use).

Restart NetworkManager
sudo systemctl restart NetworkManager

Source: https://askubuntu.com/questions/907246/how-to-disable-systemd-resolved-in-ubuntu
Date: February 30th 2021