it works very well (bootstrap-select-v1.14.0-beta3-updated and bootstrap 5.3.0)

I have modified the file bootstrap-select-v1.14.0-beta3 and looks like working very well with bootstrap 5.3.0, I published the source code here

https://gist.github.com/mattymatty76/c996d3b77f298b2ec133be59992df9d4

I hope this is helpful

Thank you