IOS 17.6.1 update not verifying

Not available is different from being verified. Try a forced restart:

• Press and quickly release VOLUME UP

     then

• Press and quickly release VOLUME DOWN

     then

• Hold the SIDE button until an Apple logo appears (15-30 seconds), ignoring "slide to power off" if it appears

The operative word here is QUICKLY; and try it a couple of times, the timing is a little tricky. If done correctly this will always work unless the phone has a hardware problem. 

Same problem, Update not verifying. Despite repeated forced restarts, deleting and re-downloading the update multiple times. Never had this before ever. Multiple users on Reddit reporting same issue.

iPhone 11 pro