How to use my Mac Mini WITHOUT being connected to the internet

I have a 2014 mac mini, an iPhone and an apple watch. These are all for personal use only.

I had problems with a cyberstalker before I got the mac mini, but I know the cyberstalker got access to the mac mini, so I decided to back up and reset to factory settings. I realize that I lose access to the backup while off line.

I’ve been dealing with keyboard compatibility issues in the reset because I blew past the “reinstall os system” without thinking. That’s not so much the issue as hoping I can have access to all the software after the reset without connecting to the internet. No internet, no cyberstalking.

I don’t mind having outdated software. I just need a safe place for my pages documents.

I’m just afraid that if I go online to download the updated os that I open myself up to this hacker again and end up back at square one.

The phone and the watch seem to be less of an issue.

I just need a “clean” computer for private documents.

Help!