I bought a monitor since the smarts in my smart-tv died, making the entire display unusable. Now I wanted to use a separate SBC for smarts in the "dumb" monitor. I would have gone for a modded fire-stick, but Amazon in their infinite wisdom, sunset all versions except the 720p potato and the smart-speaker-cube. I'm currently using a RaspberryPi 4 and looking at argon one for a remote control case. Googles widevine does limit the DRM on some content I "own" though. With Amazon on course to EOL the more sane sticks, are there any well-moddable streaming-sticks/boxes, that bring the relevant codecs and DRMs?
From what I've seen, the argon does passive-cool alright too. With Flirc I'd need to keep the mini-HDMI-dongle and buy a separate IR dongle, that takes up a usb-slot and doesn't have a low-power MCU. My Pi is currently in a no-name passive-case already. Unless I misunderstood you, I don't see the advantage.
It sounds like my case recomendation doesn't fit your needs. However, the rest of what I said still stands