The Beelink R89 is the player that produces the 4k signal.
When I remove it, there is no signal.

When I put it on 1080p I get a nice 1080p signal on my TV through the HD621.

When input it on 2160p it only works direct to the TV, via the HD621 I get artifacts.

Meridian G68 AXV, HD621 | Cinepro 2k6mk5 | 4x Scanspeak A4 monitors, center & 26W Sub | RPi Hifiberry digi+ | Roon