Android does some estimations based on battery behaviour to make the percentage display more accurate.
This is just the user facing component, of course, but “50%” doesn’t mean much if the displayed percentages aren’t compensating for an older battery losing the last 25% of its charge in a few minutes because the cells are degraded.
I don’t know if there’s anything like that on desktop Linux, but I certainly wouldn’t say calibration isn’t a thing anymore. It’s just done automatically and hidden from the user.