You can add ssh and video=HDMI-A-1:1920x1080M@60D to boot params in uEnv.ini and see if that helps? - The first forces the SSH daemon to start on boot so you can find the IP from another device and log in. The second forces the initial DRM state to 1080@60 output; sometimes it will run at 4K and TV's don't always agree with that. The display.service failure is harmless; this is from the VFD driver service (it fails as the U9-H has no VFD display IIRC). It has absolutely nothing to do with HDMI output.
The LE13 images here: https://chewitt.libreelec.tv/testing/ run a newer kernel with some changes to HDMI/DRM things. You'll also find a U9-H image there (for eMMC install) but mainline u-boot support is still in a rather experimental state and when you hit issues with that image I have no time or interest for bug-hunting right now, so I would suggest sticking with the box image on SD card so that vendor u-boot is used. As much as I loathe vendor boot code it's probably doing a better job with that hardware.