I have downloaded my explorer edition and, the moment I get past the loading screen, the menu appears completely textless. I've also tried clicking around and the new pages that pops up, such as the option menu, also is totally textless.
I will appreciate any help, thank you in advance.

Take a look at this discussion at the official twitter. Someone else had similar issue and they managed to solve it. Maybe if you follow the advice there, you can fix it too untill official patch for this comes out.

https://twitter.com/OwlcatGames/status/1044592995797016577

Also, there is similar topic in this forum named invisible test in menu (its a typo, it should be text not test). Maybe the answers there will help you aswell.

https://www.gog.com/forum/pathfinder_kingmaker/invisible_test_in_menu