I'm in my early 40s, and I've never had a job where we've "hot-desked" like that, even when a company was out-growing an office.
Every job I had before COVID back to when I started back in the early/mid 90s had dedicated desks.
Still a net positive in my experience.
My workplaces have not had gyms, but I bought equipment for my home that maintains the streamline. I haven't been perfect at my routine because my work schedule isn't consistent which is annoying, but I do still get some exercise in at least twice per week with it. I doubt I'd be getting at least that otherwise.
Some people simply have no regard for others and will mess with or jack your shit. Don't give them the chance.
Go ahead and leave a coffee mug, who cares if you lose a coffee mug?
I spend in the office more time than at home so I want a nice environment.
Many humans like to decorate their desks, keep personal stuff there. It's normal.