All these standard Bootstrap 4.6 things should work everywhere in the Magento 2 shop.
The styles are working, but the JQuery does not. So the goal ist to fix this problem.
We tried to add popper.js and bootstrap.xxxxx.js in different ways,
but without success. BS4 was not working so we removed all our code, now the template is as how we got it.
CSS things like spinners work fine.