Just an update to this:
I previously recommended
this HDMI splitter, which does successfully allow the Mini Monitor video feed to show up on the LG:
However I discovered that this unit apparently does not pass audio through to the LG TV. I tested it on a CX and a C9, and could not get any sound through this box when fed by the Mini Monitor box.
I finally got everything to work by feeding the Mini Monitor SDI output to an AJA Hi5 box, then sending the RCA audio outputs of the Hi5 to my audio mixer. The HDMI output of the Hi5 then goes to the LG.
Another much cheaper device that I successfully tested was this $25
J-Tech HDMI audio extractor, which functions exactly like the AJA Hi5, except that it takes an HDMI input, instead of SDI.
Resolve Studio 18.0.2 / Decklink Mini Monitor / 14" 2021 Macbook Pro Max (macOS 12.5.1, M1 Max) / 32GB RAM