When you go to disable - or enable guided access for the first time an overlay shows. One of the options will be literally options on the bottom left.

Tap that and then you’ll see a new screen with a bunch of toggle switches on the bottom. One of them will be called Touch. Disable this and then touch is disabled.

I say this because I use it all the time for my kid but the options should keep the same for each guided access session. So you shouldn’t need to be going into options each time - only enabling and disabling as I mentioned in my previous.