sudo nano /etc/NetworkManager/conf.d/default-wifi-powersave-on.conf
And change wifi.powersave to 2
or
sudo sed -i 's/3/2/' /etc/NetworkManager/conf.d/*
Possible values for the wifi.powersave field are:
NM_SETTING_WIRELESS_POWERSAVE_DEFAULT (0): use the default value NM_SETTING_WIRELESS_POWERSAVE_IGNORE (1): don't touch existing setting NM_SETTING_WIRELESS_POWERSAVE_DISABLE (2): disable powersave NM_SETTING_WIRELESS_POWERSAVE_ENABLE (3): enable powersave
References
https://askubuntu.com/questions/1403773/22-04-wifi-keeps-disconnecting-for-a-few-seconds-frequently
https://unix.stackexchange.com/questions/269661/how-to-turn-off-wireless-power-management-permanently