Some phones bypass the battery when plugged in, but not all do. I know it's advertised as a feature of some gaming phones because graphics-intensive gaming is one use case where you'd want to use the phone heavily while plugged in.

Even then, some phones that advertise bypass charging are actually using a software-based implementation, and they can still end up with swollen batteries after being plugged in for extended periods.

Steamdeck lets you set your preferred % and the dock does pass through charging/power, which I love because that combo guarantees the longest possible life for the battery. I turn it back to 100% for flights, otherwise leave it as 80% at all times. Mine is almost 4 years old now but I don’t feel even a hint of battery degredation yet.