PLEASE HELP - trying to use old macbook pro as a external display - not working

Hi i've never posted in here but i'm desperate. I've been attempting to start a streaming channel and i've run into every issue imaginable along the way. The latest is that I purchased the new M3 macbook pro and i want to use my old 2015 macbook pro as a display screen. The OLD macbook wont pop up when I go to the display settings in the new mac. However, the new mac pops up in the display settings on the old mac (but this is not want i want to do). I also tried using a traditional HDMI cord in both devices and a USB-C HDMI. Nothing worked.

What i want to know is:

  1. If the new M3 macbook pro is capable of supporting an external monitor (the system manual claims it is)
  2. And if so, how do i turn my old mac (or any external monitor for that matter) into an external monitor.

PLEASE HELP - thank you

PLEASE HELP - trying to use old macbook pro as a external display - not working
 
 
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