airplay in imac2017

alk281 wrote:

Updated my iMac 2017 with MacOs 12.0.1, but Airplay is not supporting to use of iMac as external monitor for MacBook Air M1.

Correct. You would need a 2019 or later iMac.

Any future plan to release airplay for iMac 2017 or older iMac models.

No one here can speak for Apple, but it's doubtful.

or any other ways to use iMac 2017 as external monitor.

You can see if Duet Display works.

https://www.duetdisplay.com/

Were you able to AirPlay content from your MBA to your iMac with Big Sur or earlier systems?

From this Apple document, Use AirPlay to stream video or mirror the screen of your iPhone, iPad, or iPod touch - Apple Support, the following text indicates that it's not possible between Macs.

Use AirPlay to stream or share content from your Apple devices to your Apple TV or AirPlay 2-compatible smart TV. Stream a video. Share your photos. Or mirror exactly what's on your device's screen.

The real answer is Apple doesn't support AirPlay to 2017 iMacs (except Pro).

Target Display Mode has been dropped by Apple. Only a few older models were able to be used that way.

Others have asked that and there are 3rd party solutions available but are reported to be rather slow.