In my case I have a similar problem, in the development version the css and js (assets) are not loaded by default, to do so you have to follow the ones described below ...
https://devdocs.prestashop.com/8/development/compile-assets/
for the "front office" it seems to go well but for the "back office" it only works on the main page, when I go to an internal section (but for example orders, products, ...) it appears without styles
Does anyone know how to solve it?
..finally I have seen that I needed to perform
"npm install" and "npm run build" in the folder
"admin-dev / themes / new-theme /"
and now it's going well
Thank you.