I tried to figure out what might be broken. I think it is because the usage has changed, compare:

• https://getbootstrap.com/docs/5.3/components/popovers/#usage
• https://getbootstrap.com/docs/4.6/components/popovers/#usage

At a minimum, the JS file will need to be udpated:

• https://github.com/google/docsy/blob/main/assets/js/offline-search.js