How is the external display connected? I have never seen Freesync over HDMI work. The early implementations were AMD proprietary and the new ones require HDMI 2.1 which has some ridiculous bullshit about not being implemented by open source drivers. HDMI sucks, use DisplayPort if possible. If your laptop doesn’t have a DisplayPort connector, try a USB-C to DisplayPort cable, as usually the type C ports on laptops support DisplayPort alt mode.
Linux on phones and tablets is a thing. Typing from my Xiaomi Pad 5 Pro running postmarketOS and LibreWolf.