Your keys must be the same version as (or newer than) the firmware. If you try to install Firmware 18.0 using keys from version 17.0, the installation will fail because the emulator can't decrypt the new firmware package.
Ryujinx might be unable to "write" the firmware files to your disk if it’s blocked by Windows security or placed in a restricted directory. ryujinx can't install firmware
If Ryujinx "can't install firmware," the issue typically falls into one of four categories. Your keys must be the same version as