There's no hard and fast rule. It's all about airtime rather than client count.
There's technologies that theoretically maximize the amount of available airtime for clients (Eg. MIMO) but it may not always see real world benefits as much of it is clients based.
Finally, there's the amount of data a given client is trying to transmit and how frequently/infrequently they will be needing airtime to transmit/receive.
I've always really liked this video as a good explainer of some of the basic concepts and calculations: https://youtu.be/U31fQGCsmKk?si=rUHOU32H463jEEzj
All this boils down to, overspec or understand your requirements very clearly and engage a wireless professional.
Personally, for a typical office based working area, my rule of thumb is ~25 devices per AP.