Note that fkms has long been deprecated and is not supported any longer.
Don't use it to try to workaround whatever problem you have.
Start with using the current LE13 nightly with unmodified config.txt and make sure your bootloader is up-to-date (Settings->LibreELEC->Updates, reboot after enabling the update).
If this doesn't work remove the SD card, powerup your RPi and check the "display line" of the diagnostics screen.
Next to DISP0: HDMI you should see HPD=1 and EDID=ok.
If you see HPD=0 this means the hotplug detect line isn't working which is usually caused by a broken case (esp Argon One are well known for this problem), HDMI cable or HDMI adapter or HDMI port on the TV.
Test without the case, with a different HDMI cable and a different HDMI port on your TV.
so long,
Hias