TOPIC:

I searched to find a proper answer to this. If I read right I think it isn't possible to use my 2017 5k retina iMac as a second monitor with Mac Studio. Can someone confirm this.

Thanks.

support.apple.com/en-us/HT204592
Only older iMacs between 2009 and mid 2014 and only with High Sierra or earlier
Target display mode is a feature available with certain older Mac models.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
To use any of these iMac models as an external display:The iMac used as a display must have macOS High Sierra or earlier installed.The other Mac that you're connecting it to must have been introduced in 2019 or earlier and have macOS Catalina or earlier installed.The cable connecting the two Mac computers must be a Thunderbolt or Thunderbolt 2 cable.

24-inch and 27-inch iMac models introduced in 2009 and 2010
To use any of these iMac models as an external display:
The iMac used as a display must have macOS High Sierra or earlier installed.The other Mac that you're connecting it to must have been introduced in 2019 or earlier and have macOS Catalina or earlier installed.The cable connecting the two Mac computers must be a Mini DisplayPort cable.

See this as well

9to5mac.com/2022/07/04/use-imac-as-monitor/

Luna Display and Duet Display are two of the top options.

Luna Display does require a $119 Luna Display USB-C dongle but has no subscription cost.

Duet Display doesn’t require any hardware but goes from $25/year for Duet Air

Duet Air looks promising. Thanks.
I will be trying it out.

Duet doesn't work with Mac Studio. They are working on it.
As for Luna. In my case getting a second monitor is not a big difference cost wise.

It's frustrating how difficult this is. BTW Apple's handling of monitors is one reason I opted for a third-party display over the Apple Studio Display for my Mac Studio. I need a monitor that can be switched from my Mac Studio to my MBP to a Windows PC as well as a second monitor for my iMac Pro and do so without having to keep pulling out the same cable.

I need a monitor with multiple inputs and that's just not how Apple makes their monitors. By the way, I also have a 2017 iMac Pro that can't be used as a second monitor for the other computers. It's a major disadvantage of Apple monitors often needed by multi-computer users and rarely discussed IMHO.