Because an eV is a unit of energy (1 eV = 1.602e-19 Joules). It's defined as the kinetic energy of an electron that is accelerated by a potential difference of 1 Volt, nothing to do with its rest mass.
When rest mass is stated in energy units such as eV, they're calculating it using E=mc^2.
Yep, archlinux with gnome 48-testing with experimental features enabled to allow VRR, as well as fractional scaling. I prefer using my 2.8K display at 150%. Appears to be working fine with everything I've used. I have had some issues with wifi cutting out intermittently, but I think that might be a misconfiguration of roaming on my APs kicking the laptop too eagerly.
power-profiles-daemon works well, I didn't like how much the battery drains overnight on the s2idle suspend mode, so I've set up a systemd unit to hibernate after 30 minutes of sleep.