How to transfer my photos from my old mac mini to my new mac mini?

The fastest, easiest and best way to migrate to your new Mac Mini, is to connect your old Mac Mini’s Time Machine backup to the new Mac Mini and migrate everything during the initial setup.

If you do not have a Time Machine backup for your old Mac Mini?

Then you really need to get a USB external hard drive and make a Time Machine backup of the old Mac Mini, that way you can migrate from Time Machine when you setup the new Mac Mini.

see > https://support.apple.com/en-us/HT203981

Your welcome.

Careful not to buy the cheapest one off the shelf. For what it’s worth, if you only have the choice between a Seagate Slim and a WD Passport, go with the Seagate. Likewise if they have something better, go for that instead.