The solution to Ubuntu 20.04 internet slow down after suspend or screen lock

One thing I've noticed on Dell XPS 13 running Ubuntu 20.04 LTS is that the internet grinned down to a halt after waking up the computer from a suspended state (e.g. after locking computer).

The solution

Prevent Wifi sleep mode.

$ cat /etc/NetworkManager/conf.d/default-wifi-powersave-on.conf
[connection]
wifi.powersave = 3

• pico /etc/NetworkManager/conf.d/default-wifi-powersave-on.conf.
• Change WiFi.powersave from 2 to 3 (Enable power saving).
• If it's already set to 3 try setting it to 2 (Disable power saving).
• After saving the file run sudo systemctl restart NetworkManager

Reference