Expected behavior

Invalid form should not be able to close dropdown

The classic bootstrap validation should be working

Actual behavior

I have created a dropdown with a FORM. Inside the dropdown form, there is a required field, when I try to validate the form with no value in the field, I get an error but the dropdown closes and the form diseappear. This should not happen while the form is not validated

also, I have tried the classic bootstrap validation and copied the code from

https://getbootstrap.com/docs/5.0/forms/validation/

but the code is not working, why ?

Resources (screenshots, code snippets etc.) https://mdbootstrap.com/snippets/standard/alexis_comte/4765673

Test page available on https://www.affection.org/test/d.html