I have encountered this use case multiple times where teams want to change their working days (weekdays + weekends) instead of them being the default.
Another thing that I identified was that the Gant Chart view doesn’t count weekends in duration. Ideally if task due dates are spanning across the weekend it should be accounted for.
There may already be separate posts (that’s better) about these two topics in Product Feedback and it would be good for you to vote there and see if any workarounds are offered.
Thanks,
Larry