iMac as a second display

Hello, b_sid.

Unfortunately, no, you cannot. The 2020 MacBook Pro is too new and the macOS on it is too new, as well.

Here are the rules for Target Display mode on iMac:

click> Use your iMac as a display with target display mode - Apple Support

Target display mode is a feature that was available only with certain older iMac models.

Only the following older iMac models can be used as an external display when plugged into another older Mac model:

• iMac models introduced in 2011, 2012, 2013, and mid 2014 using Thunderbolt or Thunderbolt 2 cable.
• 24-inch and 27-inch iMac models introduced in 2009 and 2010 using Mini DisplayPort cable.
• The intended target iMac must be running macOS 10.13 High Sierra or earlier; it does not work with macOS 10.14 Mojave or later, or with Boot Camp and Windows.
• Retina display iMacs won’t work as target displays.

• In all cases the source Mac that you're connecting FROM must have been introduced in 2019 or earlier and have macOS 10.15 Catalina or earlier installed.

FWIW, Apple started the deprecation of TDM with the elimination of TDM capability from the Late 2014 iMacs. They administered the coup de grâce to end its misery in Early 2020. Before COVID. TDM was always an "iffy" function, especially with supported iMacs made between Mid 2011 and Mid 2014. Even the support article was archived before the 2020 models came out. (It was reactivated in May of this year).

What has been frustrating for the volunteers here is that, before COVID, we probably saw one TDM question a week. With work/study from home, it jumped to a dozen or more a day.

I believe some struggling journalists—and I use the term lightly—spewed forth internet articles saying any iMac could be an external monitor for any other electronic device. Their lack of editorial assistance was compounded by a fatal lack of desire to research diligently.

Based on unvetted articles, people bought expensive cabling and even computers that would not work with TDM, then came here to complain to Apple.

Any conventional external monitor is a much better solution for most people. They are cheaper, use inexpensive cabling, use far less power and, unlike an iMac under TDM, allow extended desktop mode and well as mirrored.

As these forums are not the venue for discussion of Apple policies and decisions (see ToU Section B.1.ii), please use this link to express your concerns directly to Apple; they will not see them here:

https://www.apple.com/feedback/imac/

doesn't work with their newest Macbook model, despite having all the same outlets.

I would not mention taht to Apple because TDM function is not based on ports. You position will be stronger by omitting that bit.