We have an issue on the below pages, the FAQ accordion do not collapse anymore and we cannot find the reason why. We have checked everywhere (blocks, views…) and nothing works.
Thanks for reaching out, and apologies for the late response.
jQuery is no longer part of the Drupal Core. This means that you need to install it separately. Whilst this has been included in the CERN Drupal Distribution, it is not actually applied to your website specifically. You would need to install first https://www.drupal.org/project/jquery_ui and then https://www.drupal.org/project/jquery_ui_accordion. This should allow you to restore functionality.
The newest release of both modules are compatiable with Drupal 8 and Drupal 9.
It is important to accentuate that since jQuery UI is no longer actively maintained, it is unlikely that a version compatible with Drupal 10 (or even PHP 8; PHP 7 will reach end-of-life come November) will be released. As such, whilst you can re-create the functionality you desire with the modules currently available, we simply cannot guarantee that said functionality will continue to work. As such, I would encourage you to explore alternatives between now and November.