It's best to be free and have an app store that offers Disney +, Netflix, etc. So best Android TV, but unfortunately for some reason this no longer works on Pi 4.
And, alternatively, a Raspberry Pi 3 would be enough for Android TV, it seems to work fine there, but 1GB RAM.
OpenElec https://openelec.tv/
OSMC https://osmc.tv/
XBian https://xbian.org/
Since the Raspberry has no Widevine, all of this is unusable. With Netflix and co you will not get any HD, just SD content.
A smart tv requires considerably more than a processor with an operating system. If you want to build it yourself, this includes first of all the HF technology of the TV reception and the other hardware of PCs, which is also necessary for the minimal equipment of a raspberry
USB, Ethernet, WLAN PVR etc.
And how do you want to see a picture?
