Using a 2010 iMac 27'' as second display for a 2017 5K?

I have an older 2010 iMac 27´´ sitting now right next to my 2017 5K.
I know this

paper from Apple about using the 2010 as a display with target display mode, and as I am running Monterey on my 2017, this seems to be not an option anymore for me.

So, does anyone know an other, really working, way to use the 2010 as a second (or in my case rather 3rd) display for my 5K?

The only “reasonable” option is Luna Display, which has been reported to be “laggy”. There are “unreasonable” options, though…

Luna Display requires a Modelyear 2011 or later, so it will not work in my configuration.