I am entirely unhappy about this issue as well. Ever since the Josh Strobl split and began working on Budgie separate from Solus I've found that my computing experience has sharply declined.
That said here is an idea: Switch to Dolphin from the Flatpak Store.
There are existing issues with using Dolphin that my roommate and I found ways to overcome. They can be found in this link.
Also if you have issues with any theme not sticking on a Flatpak app here is a possible solution.
I suffer from a genetic disorder that is slowly causing me to become blind. The sharp blinding white from the Files causes me extreme discomfort. My eye has started to go lazy since this issue began because of the extra time I had to spend figuring out ways to view my files .