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Could just set up an app password limited to accessing gmail, been able to do that for like 10 years now and it's not going away with this change
different password: check
ringfenced access: check
Not sure why there'd be a dropdown to select the service if not, maybe I misunderstood
E: I misunderstood, you're correct. The dropdown is for your reference (e.g. "Mail [on] iPhone") and if you select "Other" it's the same as selecting the other dropdown's "Other", it lets you type a custom name. Guess that was never as secure as I'd thought!
I've long since moved to Fastmail which does do the limiting by service, thank you for correcting!