Accented characters with bluetooth keyboard

Hellooo.

In my SwiftKey set-up I use multiple languages - English(UK)/Polish, Japanese. I also use a bluetooth keyboard (Fintie brand).

I am struggling to type in Polish using this set-up, as I cannot use the accented letters. Ctrl + letter does nothing, Alt + letter gives ridiculous results (like the German ß being inputted, instead of the Polish ś, despite me not having installed a German language).

Is it something I am missing, do I need a different key combination, or is it impossible for me to use accented Polish letters using my bluetooth keyboard with Swiftkey?

Thank you