Using late 2012 iMac 27” as a display with a new, 2023 iMav

No, not with Target Display Mode (TDM). The last Mac computers that could use a TDM-supported iMac (like the 2012 model) as a monitor were the 2019 models, and they could not be running any macOS version newer than macOC 10.15 "Catalina."

The very restrictive hardware and macOS requirements of TDM are laid out in this Apple article:

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

That may the option for a third-party screen-sharing solution, but most are reported to be "laggy."

Apple started the deprecation of Target Display Mode in Late 2014 and threw the last shovel of dirt on its grave in early 2020.

As Allan has stated no, what you are asking is not a viable solution. If you want the best (and least expensive) solution, simply purchase an external display. The reason I mention it is the best and least expensive solution is:

1. No expensive cabling or third party apps are required.
2. Dead simple to connect and set-up.
3. Overall the most reliable solution.

Finally, please remember that Macs are computers, they were never designed to be external displays for other devices.

Your welcome.