Drupal 11 error: Bootstrap's JavaScript requires at least jQuery v1.9.1 but less than v4.0.0

I don't think that's going to be that easy to support, more or less the Bootstrap 4 and Radix 8.x-4.x have reached their end of life.
One thing I can think of is to override jQuery version via theme libraries using libraries-override if that would work. Alternatively, consider loading a certain jQuery version with a custom hook_page_attachments_alter

I mark this as closed (won't fix) since there isn't much we can really do here, but please, if you come up with a solution, do share it here for others.

Yup, makes sense.

I found the module https://drupal.org/project/jquery_downgrade that I'm gonna try to limp along with for now.

I haven't thoroughly tested, but at least some of my pages appear to be rendering properly now and I'm not getting a console full of javascript errors.