MacOS High Sierra update to New Computer

I see some of my text got cut off. Below is the correction, please read it fully. Also, note that Servant of Cats is also correct when he notes 32 bit applications will not migrate. If you have any (if you don't know how to check, please ask) then either update them or upgrade to 64 bit apps which will migrate!!

·      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. 

Your data files will transfer – but if you have any 32-bit applications that you're running on that Mac, those won't run on a new Mac, even under Rosetta 2 translation. iTunes and Photos libraries may undergo one-way conversions, so if you're paranoid, you could keep backups of the libraries as they existed on the old Mac until you are satisfied that the conversions proceeded smoothly.

Catalina and later replaced iTunes with separate applications: Music, TV, Podcasts, Books, and the Finder.

Yes, you'll be able to migrate all your data from an iMac using macOS High Sierra to an iMac using macOS Sonoma (the current latest version of macOS).

You'll have a choice of transferring your data either directly from Mac to Mac or by using a Time Machine backup. For more informations: Transfer to a new Mac with Migration Assistant - Apple Support.

If, instead of making Time Machine backups, you've been making bootable clone backups (using Carbon Copy Cloner or SuperDuper!), those will work as sources for Migration Assistant, as well.

Yes, they will transfer just fine. Please read below!!!!