@extend .float-end selector not found

[tex0gen]

Hey, I've asked in a few places with regards to this now and no one can give an answer at all.

I am trying to use V5 SASS. I import each file from bootstrap and then later I use..
@extend .float-end
Or
@extend .btn-primary
But my SASS errors with ".float-end selector not found" or btn-primary respectively.

This was previously working with bootstrap 4.5. Is this a change in the way these classes are generated? What am I doing wrong? Is there another way around this if I can't use extend any more?

To see the setup of the main sass file, see here: https://github.com/tex0gen/bootstrap4-wordpress-theme/blob/bootstrapv5/assets/sass/main.scss

Any help much appreciated.