I have a new iMac (24-inch, M1, 2021) and an iMac(21.5-inch, 2013) which runs High Sierra 10.13.6.

I have a new iMac (24-inch, M1, 2021) and an iMac(21.5-inch, 2013) which runs High Sierra 10.13.6. My Command+F2 does nothing to enter target display and I have purchased every dongle/adaptor since my new iMac has only thunderbolt cables - nothing works to enter Target display mode. What am I missing? I am using the original keyboard and I have restored the defaults. I have used Command+Fn+F2 and unchecked it as a standard function key. I have restarted both computers so many times.

The old iMac works just fine. Should I sell it? I'd rather use it as a monitor instead.