How can we make 2017/27" iMac a monitor for 2019/16" MacBook Pro ?

If you run Monterey on both the iMac and MacBook Pro you can AirPlay one to the other.

Sorry but that cannot be done as both computers are too new. Please refer to the link Mal-S provided. If the MBP needs and external display your best option is to buy one. This is FAR more reliable and much easier to setup then TDM ever was, in addition it does not require expensive cables to make the connections. You can find good quality external displays in the $100-150 range.

While Airplay may be an option (assuming both are on Monterey) it may not provide everything you need as it only mirrors on the external display what is already on the primary display.

It is no longer possible.

rkaufmann87 wrote:

While Airplay may be an option (assuming both are on Monterey) it may not provide everything you need as it only mirrors on the external display what is already on the primary display.

Actually that's not the case. You can mirror the display or use it as a separate display.

You can't.

See this link.

https://support.apple.com/en-us/HT204592

Welcome.