Option show only once enables "Don't Show Again" checkbox.

I was testing, I have drupal 10. I followed your instructions to replicate the error, but I couldn't.
Everything seems to be correct, can you provide a little more detail of the error? What version of Drupal do you have? or if you have some module/theme that can interfere with the proper functioning of the module?

Been testing in my local:

• Modal page 5.1.0
• Drupal 10.4.8
• php 8.3

And in my case I cannot reproduce the issue. See image

We should close this ticket as cannot be reproduced.