In my experience, calling a manager at work "Mr" because they're your manager, is very old-fashioned indeed.
The only instance I've encountered it was with a non-executive director of a firm, who was by then an elderly man (some decades older than the oldest executive staff) who had status in the broader local community and who had a patrician outlook. The actual managing director was not accorded the same reverence, nor capable (by his character, moral outlook, or community status) of commanding it.
It should also be mentioned that when it was common in a workplace to call colleagues "Mr", it would also have been common for management to also call their peers and subordinates by their title unless they had become close and were relating to one another informally (whereupon peers would use first names mutually, and a manager would refer to subordinates by their first names).
That is, in the past the default form of address was to call all other adults by their title, and to be addressed by first name was a sign of a climbdown into informality between people who knew each other.
If there was a difference in social status, a superior would have first asked a subordinate if they could be called by their first name, though the subordinate may have continued to call the superior by their title.
It would have been presumptuous for a superior to call subordinates by their first names without asking, unless he had already asked to be called by his first name himself (a general practice which some may have indulged or preferred, but which a minority in that era may have found over-familiar).
So unless you are generally being referred to as "Mr" in the workplace, it's generally safe to assume that first names should be used in the modern workplace.