2024 mac mini slow since using apple display

Looks like spoilt goods to me. I would reset the Mac to factory What to do before you sell, give away, trade in, or recycle your Mac - Apple Support taking care not to involve Time Machine during the entire process.

Manually save user data like pdfs, jpegs, docs and the like to external disk and copy them back later. You can also use iCloud which will also save your bookmarks. iCloud Subsrciptions are monthly so feel free to cancel later.

Finally, install apps afresh after the reset procedure is complete. Do not to install any dodgy 3rd party apps like the ones you did previously.

Good luck!

Do you any 3rd party apps that claim to enhance performance, clean viruses/malware/monitor temperatures/perform disk/cpu/internet speed tests or scan your system for various reasons including reporting?

Start with a better description - what does slow mean exactly?

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