Re:Why the Gov.uk Design System team changed the input type ...
by brlewis on Thursday February 27, 2020 @11:25PM
(#22440509)
TBH I went on autopilot looking at MDN's browser compatibility list. Also as a user of Firefox on Android I was interested in something that works there, but type="tel" doesn't behave any better. The only advantage to not using inputmode is getting rid of an HTML validator warning, so you're right.
I apologize if you already know this, but to make sure we're on the same page: what "inputmode" does is tell phones to display the onscreen keyboard as a numpad, instead of a full set of QWERTY letters and numbers. Outside of a few edge-cases, you don't generally need that on desktop.