Trouble using Luna Display

Has anyone had success using the Luna Display to use an old (mine’s a 2013) 27-inch iMac as a display for a new M1 MacBook Air in clamshell mode?

Connecting via wifi gives horrible latency (text vibrates, blurs and pixelates when I slowly scroll web pages).

So I’m trying to connect the two Macs by Ethernet, as explained at How do I use a USB, Ethernet, or Thunderbolt connection? - Knowledge Base in the “Computer-to-Mac Mode” section. When I did that, it connected briefly, but then the big display went to the black “ready to connect Luna” screen and I can’t get it to connect again.

I also noticed that in wifi mode, “sleep display” doesn’t work, so MacBook display appears to stay on continuously. That would definitely be a deal-killer.

I wrote Astropad and they didn’t address my issues, saying they were a small team experiencing high volume, and actually refunded my purchase. Of course, I’d rather have them help me get it working than just send a refund!

Any ideas where I might go from here? Is this just too much to ask of this little hardware solution?

Should I just return the old Mac to High Sierra and try “Target Disk Mode” as mentioned at Using Old iMacs As Display For Laptop - #2 by tjluoma ?

Thanks,
Russell

The Apple page on Target Disk Mode says, “The other Mac that you’re connecting it to must have been introduced in 2019 or earlier and have macOS Catalina or earlier installed.” So that means my new M1 won’t work for that. Looks like Luna’s my only hope???