The only thing that hits me as remotely strange is the fact that you have 120VAC between the black hot and the black load. But I’ve never tested between those two conductors. You’re bridging the connection to the light so 120 VAC may be normal.
I can’t see into your box to get a better sense of your connections, but from what you described this should be the proper wiring. Pigtail a white conductor to the white bundle and connect that to the neutral terminal. Black hot to line terminal. Black load to load terminal.
I think I might have a bad red dimmer → I could never get it working correctly in the past and kids were out of town so I gave it a 2nd go. I just tried a different circuit in the house and it only powers on the load as well again.
I did. I ended up powering it via load/neutral off a separate circuit with no light and I’m using it as a remote switch. Still very confusing. Looks like I had it kicking around for 2 years so not eligible for warranty but still can function in some manner as a 3rd switch for my kitchen lights