iMac (Retina 5K, 27-inch, Late 2015) - as external display options?

Hi everyone
How can I use/connect my iMac 27’ Retina late 2015 as external display to MacBook Pro 14’ M1 Pro 2021?
I tried connect by cables:

  • Mini DisplayPort 4K 60Hz → USB-C (compatible with Thunderbolt 3)
  • Belkin 4K Mini DisplayPort → HDMI
    and it doesn’t work.

I’m afraid you cannot, at least as far as I understand it:

So, even if I had iMac mid 2014 it won’t works, because my Macbook is too new, yes?
(The other Mac that you’re connecting it to must have been introduced in 2019 or earlier)

I don’t know any more than what’s written in that article, but as far as I can tell, your understanding is correct.