Hi @richardesignerUK,
Thanks for reaching out. That sounds really frustrating, especially on such a powerful new Mac Mini! To help troubleshoot, could you please confirm the exact versions of Illustrator and macOS you're using? Also, does the high memory usage happen right when you launch Illustrator, or only after opening a document? If it's with a document, does it occur with all files or just a specific one?
Please try resetting Illustrator's preferences, but be sure to back up your preferences before doing so. Here's how: https://adobe.ly/438BDan. After resetting, check if the memory usage improves.
Also, try running the system in Safe Mode and test with a new local admin user account to rule out system- or user-specific issues. Here are the references:
https://adobe.ly/43qIudY
https://adobe.ly/4mwgHSm
Let me know how it goes or if anything changes after trying these steps.
I'm here to help and look forward to your update!
Abhishek