@Substring I tried installing NOOBS, adding recalboxOS-rpi3 to the os folder of NOOBS. Install went ok. As soon as I boot into recalbox, I still get the "input not supported" error on the display. I confirmed that Raspbian outputs to display and works normally on this same hardware. Maybe there is a display driver issue in the new version of recalbox?

I used the instructions here: https://github.com/recalbox/recalbox-os/wiki/Setup-a-dual-boot-raspbian-recalboxOS-(EN)
And used the 4.1.0 recalboxOS zip found here: https://github.com/recalbox/recalbox-os/releases

I tried a fresh install of 18.02.09 and it appears to not boot (red and green led's on the pi light up and stay illuminated). I found a "config.txt" file in the imaged SD card's main directory. I uncommented the following line:

#uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1

Then recalbox appeared to boot, but the output to the monitor was glitchy (lots of screen artifacts and the image is not filling nor centered on the display) and flashed on and off every few seconds. So it appears that recalbox may be booting but similar to what @flibb said, it is outputing an incompatible signal to the display. My monitor says "input not supported" but @flibb 's TV must just display a black screen for unsupported inputs.

Raspberry Pi 3 Model B
32GB Samsung EVO Class 10 microSD card
1080p HDMI Acer display
Keyboard and Xbox 360 controller connected before powering on Pi