Amlogic s905x or s912x theoretically support 4K HDR, but not on LibreElec (see here, "4K support is experimental. 3D and HDR are not supported, i.e. they might work but I don't provide support."). I guess you could by any TV Box with these chipsets, just be careful with the WiFi chip and gigabit Ethernet (if important). My Tanix Tx7 works good (I have no HDR or 4K TV to test though).
I have a MINIX NEO U9-H and everything works just fine including HDR. Works with Harmony (Elite/Hub) out of the box. Very happy with it so far.