Anna_Aio wrote:
Do you know also if it would be possible instead of a newer model change some parts? For example use an external hard drive and run the system from there.
I am sorry I know and understand only a few things about these.
Changing parts will not change the answer as to the highest version of macOS you can run: Monterey. But if you would like to install Monterey on an external drive, and run it from there, you can do that.
For someone who only had a mechanical HDD, or Fusion Drive, installing macOS on an external SSD and running it from there might be a way of improving performance. I could be mistaken, but it looks to me like your iMac has an internal SSD which would be faster than any external USB 3 / SATA SSD that you could buy.
In any event, I would recommend backing up your system before you install Monterey.