For maximum compatibility with all services you are limited in your choices due to DRM licence requirements.
You can mostly decrapify android based boxes via ADB to strip out much of the bloat, strip most of the telemetry entirely then block the rest in your firewall, and replace the launcher with a super barebones one like Flauncher but it will never be 100% perfect.
If you must be in full control of what is on the device and what it is doing, a small, low powered miniPC (intel n100 is a good chip for basic AV for example, 4k 10bit with perfect H265 and AV1 decoding) and use the operating system of your choice, but you are then limited in what you can stream via browser or third party apps, often in nowhere near full quality, again this is due to licencing and drm.
The best option is to avoid streaming services altogether and download your own content, then use an offline player like kodi or a server/client solution like Jellyfin (a free and open alternative to plex, with most of the base features well implemented) to play it.