* xsmall - Very small screens, as used in watches, wearables and other small-display devices (about <= 360px).
* small - Small screens often used in handheld devices, such as phone screens, small phablets (about < 768px).
* medium - Screens in laptops, tablets (about >= 768px)
* large - Bigger computer monitors (about >= 1024px)
* xlarge - Television screens, large projected images (about >= 3840px)

There are a few problems here:

• The small size is meant to be used on phones, yet all the available phones have 360px and so fall into xsmall
• Meanwhile, xsmall doesn't constrain the minimum screen size
• Together this means there's no constant that can work for devices like L5 or PinePhone - small means the app cannot run on it, xsmall means the app can run on even smaller screens which is not really the case
• medium is means for laptops while large for bigger computer monitors - the most common laptop resolutions are 1366x768 (mostly low-end), 1920x1080, and there's also 2160x1440@2 which means 1280x720. So laptop sizes can be 720px, 1080px - the former falls into small, the latter falls into large - so the medium description is misleading
• All values correspond to the smallest screen sides, but xlarge corresponds to the largest screen side. 4K screens are 3840x2160 - the value there is 2160px so they are still considered large, so xlarge only corresponds to 8K screens.

CC @bertob