Cemu is a Nintendo Wii U emulator. For more information, please visit the project website or view the source code.
In order to convert files to wua you can run Cemu without filesystem sandboxing from the terminal via:
flathub run --filesystem=host info.cemu.Cemu
This can be done permanently with flatseal or with:
flatpak override --user --filesystem=host info.cemu.Cemu