How do I select a menu option on my cell phone?

Contact your mobile service provider . . .

Get the user manual online. No one here knows anything about your particular device.

Can you scroll to it and highlight it and then press an enter or ok key?

I have the same trouble with received calls on my iPhone 12 mini.

It would help to know what kind of phone you have. They all work basically the same, but each brand has its own quirks. I have a Samsung which is an android. I have to clean the screen frequently because anything left behind (including too many fingerprints) will stop it from recognizing my touch. I keep a microfiber cloth in my purse just for that reason. Have you added a screen protector recently??? That can affect the sensitivity of the touch.

Have you first tried to power cycle your device?
It may not be you. Have a friend try with their phone to see if it is your issue of not.
Does this happen on all calls that require input? I have found that some IVR and Tone recognition software of the party you are calling can vary on ability.

I checked at the place where I bought the phone. I have to open up the keypad and enter the number from there.

Thanks for getting back with your answer !

Glad it worked out.