Use imac 2020 as display for Macbook Pro 2019 16"

This is not an exotic situation. I have an iMac for work and a MacBook Pro for personal use. I am using a software app called Duet to send the MacBook image to the iMac. But a wired connection would no doubt be better. It is inexplicable to me that Apple would have no interest in making iMacs and MacBook Pros work together, even if only a small number of people would have both. Apple should reconsider.

Sorry they removed that option after the 2014 iMacs & High Sirra on the Target Mac...

You can connect any of these older iMac models to another Mac from 2019 or earlier for use as an external display. Learn how to identify your iMac model.

• 27-inch iMac models introduced in 2009 and 2010: Use a Mini DisplayPort cable to connect your iMac to a Mini DisplayPort or Thunderbolt or Thunderbolt 2 port on the other Mac.
• All iMac models introduced in 2011, 2012, 2013, and mid 2014: Use a Thunderbolt cable to connect your iMac to a Thunderbolt or Thunderbolt 2 port on the other Mac. If the other Mac uses Thunderbolt 3, you can use the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter with your cable.

Target display mode requires macOS High Sierra or earlier on the iMac used as the external display. It does not work with macOS Mojave or later.

You are rather late because the last iMacs that worked as an external monitor were the Mid 2014 models. No one seems to have noticed until COVID forced work-at-home issues and people needed a bigger monitor for their notebook computers.

Before COVID we probably saw one post a week about Target Display Mode. Now we are seeing several per day, six years after Apple retired this capability from its iMacs.

Apple are not here. You can communicate your concern to Apple by using this link:

Feedback - iMac - Apple

I haven't tried it, but Turn any Mac or iPad into a second display...

https://lunadisplay.com/

Review by NAK005, you may not be happy with it…

https://discussions.apple.com/thread/251259038?answerId=252422503022#252422503022

I have the opposite use scenario. I have a 17” MacBook Pro and a 27” iMac. I want to work on my iMac while I sit in the backyard - using the MacBook Pro as my screen and keyboard. I use Screen Sharing and it works pretty well with hardly any latency. As long as you’re not going to be playing games or video editing, it might work well for you too. I’d at least give it a shot.

Interesting. I will have to try that. But I will say that using screen sharing of a Macbook Pro on an iMac screen is suboptimal. It does not take full advantage of the screen size and the resolution of the iMac. The Luna dongle and app, while I find it occasionally buggy, at least looks better when it works. It wouldn't hurt Mac to just improve the screen sharing function.

Sorry, Target Display Mode was discontinued in 2014. You cannot use your 2020 iMac as an external display. I would suggest buying an external display for the MBP.

Yes, I know my friend, less of what we want & more ways to spend money with Apple. :(