cannot turn off do not disturb

If your screen is not identical to what I posted you did not open the Control Center. With the latest version the ONLY control to turn DND on or off is in the Control Center.

Here (again) are instructions for opening the Control Center→Access Control Center on your iPhone - Apple Support, and to save the trouble of clicking the link, since you didn’t say what kind of phone you have I included instructions for different iPhone models:

iPhone X and later (iPhones XR, XS, 12, 13 and 14)

• To open Control Center, swipe down from the top-right corner of your screen (from the battery icon). 
• To close Control Center, swipe up from the bottom of the screen or tap the screen. 

If you swipe too close to the top-center of your screen, you might open Notification Center instead of Control Center.

iPhone SE (all versions), and iPhone 8 and earlier (iPhones 7, 6S, 6, 5S, 5C, 5, 4, 3GS)

• To open Control Center, swipe up from the bottom edge of any screen. 
• To close Control Center, tap the top of the screen or press the Home button.

Open the Control Center (Access Control Center on your iPhone - Apple Support) and tap the Do Not Disturb button (the one in the green circle; not the word Focus):

I don’t see your problem. Every time I tap the ROUND BUTTON (NOT THE WORD FOCUS) Do Not Disturb turns on if it is off or off if it is on. Nothing could be simpler.

Cannot turn off do not disturb

What round button?

This Focus app has been a mess for me. i missed a number of important calls. I think I have it off now. Apple, do not put things like this on our phones by default.