Read over at least these two articles concerning the M1/ARM Macs...
https://community.graphisoft.com/t5/Setup-License-articles/ARM-Mac-support/ta-p/304108
and performance:
https://community.graphisoft.com/t5/Setup-License-articles/Performance-review-with-M1-Pro-and-M1-Max...
An older Intel Mac will have a somewhat limited lifetime as at some point Apple will drop support (just as with the PPC chips years ago). But, if you have a short horizon for the machine, it might be an option? If you run virtualization software or bootcamp to run any Windows software, it would be your only option.
The 24" iMac is more of a home/student computer using the M1 chip and would be underpowered for Archicad. You should consider the M1 Max, M1 Pro and the new M1 Ultra. Your 2007 iMac has an advantage over newer iMacs in that it supports 'target display mode' ... so while it has almost no value on the resale market, you can use it as a primary or additional monitor for a new Mac.
The only options with the more powerful M1 max/pro/ultra chips are the MacBook Pro (which makes sense only if you need a laptop) or the new Mac Studio which currently has the best performance of all Macs as well as the most ports.
Do note that Archicad will not have its best performance on any of the ARM Macs until a native version is released. Currently, Archicad's Intel code is emulated by Rosetta 2...which still gives very good performance as you can see in the article above. A native version might arrive within a year I imagine for Archicad 26 or 27.
Your signature says you're on Archicad 22. If that's the case, you may not want any kind of new Mac as they will all come with Monterey and you may have issues running AC 22 there. A used Intel Mac that still has an old MacOS might be a better choice then. See:
https://community.graphisoft.com/t5/Setup-License-articles/MacOS-12-Monterey/ta-p/309154
One of the forum moderators
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB
