Call forwarding & waiting spinning

Call Forwarding and Call Waiting are Carrier features.

Not all Carriers and Plans support these features. The functions also depend on whether your SIM card is connected to your Carrier before they can be activated and deactivated. So check if you have a connection - check your Signal Bars in the top right corner. If you have a signal, try restarting your iPhone, and remember to enter your PIN code for your SIM card when it turns on again.

If you use eSIM, check if it is activated here:

Settings → Cellular → Turn On This Line must be enabled.

If you still cannot access Call Forwarding and Call Waiting, you must contact your Carrier.

I suggest that your contact your cellular carrier about that, and explain your problem.

Regards

Giulio