Need advice setting up an 'Apple Intell 19-inch' properly..

[Demanding Truth]

I'm trying to get an Apple set-up exclusive for processing mp3 music in all types of iPhone's and iPad's.. Every time I get one working it updates itself, then suddenly it doesn't work for processing music in anything.. Why?..
Do I need an Apple ID email address to use an Apple computer..?

Is there a way to block Apple computers from auto-updating/upgrading..?

I don't get an Apple ID.. They want too much of my personal private information.. Is that why something wrecks the OS..? Is it an Apple-law that I must have an Apple ID to use their stuff..? I shouldn't have to give 'a pound of flesh' to use a darn computer..

That's ten Apple notebooks that don't work now with iPhone's and music.. God save us from the rotten apple tree...

OK, so this time someone tossed out an 'Apple iMac 21.5" Desktop Intel' in super condition.. I grabbed it up at the curb.. Seems like a nice computer.. Then two weeks ago I manged to get an Apple keyboard and mouse for it from a garage sale for 5-bucks each.. oh yay...

Now I need to reset the thing to factory.. I don't want to make any dumb mistakes with this one.. What's the best approach and technique to get this thing properly reset, and working with music in iPhone's, iPod's, and iPad's..?

Will "mintyMac-1.5-Mate ISO" work in this thing with iTunes and iPhone's..?

[crewmatey]

Normally updating shouldn't really affect the functionalities you're describing, did you check if there are maybe some other issues at play?
I don't think it's because of Apple ID either, it shouldn't be required here to my knowledge.
Best way to reset is to back up everything you want to keep, then literally Wipe everything and reinstall the macOS.

You could try using mintyMac-1.5-Mate ISO, but it's heavily not recommended, there are some risks of incompatibility.

[Demanding Truth]

Thanks Crewmatey..

These ten Apple notebooks were other peoples retired old computers, free donations from a couple of small town computer repair shops.. They give me lots of free computers to cleanup and load Linux to give to disabled kids for free... I wish I had an Apple install CD...

Last year my lady's son put a crew together, and they donated huge gaming screens and game consoles to all the sick children hospitals for a few hundred miles around...

Good to hear that the music glitch it isn't an Apple ID problem.. Everytime I accidentally leave an Apple notebook on all night net-connected, it updates itself, then it stops working with iPhones for ITunes... I don't understand why...

OK, I'll just wipe this free Intel 21-inch, and hope it re-installs, then test it with a phone... I suppose I go to General, and Wipe it, and Reinstall, and just hope...
Thanks for the warning about mintymac's possible incompatibility.. The CD is now in the trash pail, and the ISO download deleted...

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