If you’re a bloke and I call you Mister, call yourself lucky. Mr means I respect you or admire you either for your seniority, your talent, or your wisdom (or all three if you’re so blessed). Mr Arnison, former Headmaster, came to our wedding but still I’d dive into a vat of bubbling tar before calling him “Barry”.
A request that I call someone by [FirstName] is processed by my external communications department. Once you’ve shared a few work shifts, come to mine for a cuppa, or, better still, washed my car, then I’ll call you [FirstName].
It might seem overly old-fashioned but the Mr adds a crashpad of comfort to interactions.
Like the polite German “Sie”, the use of Mr / Sir / Ma’am / Mrs is a custom that’s hard lost.
How else do you refer to teachers or seniors you barely know?