Cannot slide to answer a call on iPhone 13 mini

There are a few things you could try.

1. Try a hard reset of the phone. Press volume up then volume down then press and hold the power button until you see the apple logo, then let go.
2. If that doesn't work, make sure your device is on the latest iOS, and if it isn't make sure to update it.

I have had the issue for some time too.

When the issue occurs, I can only answer the call via my Apple Watch, the iPhone screen is still locked, I turn the iPhone screen off and back on, then the iPhone screen starts responding and I can only then redirect the call back to the iPhone.

This had been an issue on and off issue with various IOS version and iPhones throughout the years.

I can’t see it been fixed anytime soon.

I can't answer that but wanted to let you know that it has happened to me on rare occasions. It happened 2 or 3 times to me several years ago with an iPhone 7 and has happened once this year with an iPhone 14. It has been very rare for me but is frustrating when it does happen.

Happens to me too. iPhone 15 Pro Max with latest iOS version 17.4.1

The problem is transitory, and seems to require a core update to the phone code to fix this bug.

Apple, when are you going to fix this?