Setting up new Mac - Use Migration Assistant for old Mac / external photo library?

Migration Assistant is an all or nothing thing. You can select data, settings and apps. If you select all 3 the new computer will be exactly like the previous Mac. If you have some data files you don’t want, the smart thing to do is migrate everything then after MA is done go back and remove what you do not want. This is MUCH MUCH wiser than trying to manually migrate data. The same holds true for apps, and settings.

You could use a Time Machine backup drive to migrate your files from the old iMac to the new Mac mini. Create a fresh TM backup on an external drive with your iMac. When you get your new Mac mini, connect the TM drive to the mini before you first turn it on to set it up and when asked, choose to migrate your user data from the TM drive.

As for the photo library, that can remain on the external drive. You can direct the Photos app on the new Mac mini to launch with the library that is on that external drive. If the external drive has a USB-A type plug, all you will need to connect it to your Mac mini is a USB-A to USB-C plug adapter. You can find that all day on Amazon for ~$10.

It looks like this:



To choose which photo library the Photos application uses, press the Option key when you launch the application.

Guidance for that is here: Create additional photo libraries in Photos on Mac - Apple Support

·       Always connect your old Mac's Time Machine External Hard Disk prior to startup, this will allow a migration from your TM backup and it will be dead simple! When you start the new Mac for the first time it will startup Setup Assistant (SA), SA will get to a point where it asks if you are migrating from another computer, select Yes and follow the on-screen prompts and it's done! It is that simple! This is the easiest, quickest and most reliable method to migrate from the old Mac to the new Mac is to simply connect the old Mac's Time Machine External Hard Disk to the new Mac using a USB cable before you turn on the new Mac. 

·       NOTE 1: You will likely need a USB A to USB C adapter, you can find them on Amazon for $10 or less.

·       NOTE 2: If you have already done SA on the new computer then simply connect the Time Machine External Hard Disk using a USB cable and launch Migration Assistant (MA) which is located in Applications - Utilities - MA. Then follow the on-screen prompts.

·       The ONLY difference between MA and SA is MA will create a new user account that you need to log into.

Both SA and MA migrate applications (not 32 bit apps), data files & settings. They do not migrate Mac OS itself. Some professional apps such as Adobe and Microsoft apps may require re-installing their apps as they will not allow them to be migrated. As long as you kept the security keys for installing their apps, it is not an issue. 

Finally, never EVER use Wi-Fi when doing Setup Assistant or Migration Assistant. Why, it simply fails in most cases. Please read and follow the directions in Setup Assistant and Migration Assistant. If you do not have a Time Machine backup of the older Mac then create one! If you are not aware of Time Machine, please read Back up your Mac with Time Machine and finally if you need an External Hard Disk to use as a Time Machine External Hard Disk then many experience users on these forums prefer the OWC Mercury Elite Pro due to it's reasonable price, high level of quality and ease of use. 

Intel apps may be migrated, but they won't run natively on Apple Silicon Macs. There is a "translator" required.

If you need to install Rosetta on your Mac - Apple Support

The Apple guidance above also links to a list of compatible Apple Silicon Macs.

I use Migration assistant to move user accounts and data. I install fresh versions of applications. That way you get the up-to-date version of any apps, and they are the right version of your new machine.

Where are you moving the Photo library to? Do you want it on the internal drive of the new machine? Why not leave it where it is?

My initial thoughts mirror Yer_Man's.

Migrate your User data and settings from old Mac to the new Mac.

Connect the external photo drive to the new Mac using a USB-C to USB-A adapter.

Purchase and use a second external drive to backup both the new Mac and the external photo drive.

Can one choose which files from Time Machine to restore to new Mini during Migration Assistant? What if some of the directories (that were backed up), were synced with ICloud and Google Drive? How would one handle that?

This option is really only valid if your hard disk sizes are similar, correct? If I'm going from a 2014 mini with 1 TB to the new with 256GB it makes sense to not use migration assistant and add files needed from external hard drive or Time Machine, no? I currently have only 270 GB on my current mac and will be storing all photos and some large docs on icloud or external hard drive.

It is NOT wise at all to go from a 1TB drive down to a 256GB. ONLY do this if your old machine has at least 25% less that 256GB on it to migrate (256 * .75 = 192GB) , otherwise you will have a huge mess on your hands. We see this all the time. In other words, don't be cheap, be smart!!

Whatever you do, remember to backup the Photos library on the external disk to another external disk (apps like Carbon Copy Cloner can do this).