Cemu is a Nintendo Wii U emulator. For more information, please visit the project website or view the source code.
To get read/write filesystem permissions for converting files to wua I suggest running Cemu from the terminal via:
flathub run --filesystem=host info.cemu.Cemu
This can be done more permanently with the flatseal GUI or with:
flatpak override --user --filesystem=host info.cemu.Cemu