Allow working without Bootstrap, using the Drupal Modal (Gin)

If your theme is not base on Bootstrap 5 then there is an option to use Bootstrap CDN. If you select this option your popup will work fine.
Without Bootstrap lib ? this definitely cannot happen as you wish. It is designed with Bootstrap table library.

Thanks @lazzyvn so if Bootstrap CDN is no option and Gin is used, would you suggest forking this module or fixing https://www.drupal.org/project/entityreference_modal_create → then?

Where would you suggest to start from, with your experience? We need the functionality, but can't use Bootstrap or CDN in the admin theme.
Thank you!!

It's up to you. if you base on module entityreference_modal_create you can save your time 10% with form widget settings, or you can create a patch to add new options to the widget's config or create new widget entity_reference_modal.
You need to rewrite the js library by yourself with the same features as bootstrap table. Honestly, up to now I still haven't seen any opensource library that is as good as bootstrap-table. I think you can try with datatable or hansontable. If it's too heavy, you can write it manually as long as it can paginate the table, filter on table cell, First column have to select 1 items (radio) or multiple checkbox foreach lines. If you can replace bootstrap table library, you don't need to load bootstrap 5 cdn.