The best brand for me is Speed Queen as I find them to be the most heavy-duty and the simplest. They are commercial quality for the home. They make top-loaders with agitators and front load as well. Always a reliable unit.

Yes, many brands today make smart appliances that require a wifi connection in the home. While not necessary to operate the appliance, it provides useful features like telling you when laundry is done. The oven can be preheated remotely. Plus, brands like GE have now added cameras in their oven cavities. So if you’re truly bored, you can watch food cook. Even Google and Alexa can control appliances, “Hey Google, preheat oven to 350”.
That’s not where we are headed. It’s where we are! Don’t be afraid of the words smart or wifi as many units. You can just bypass that feature by not connecting. However, brands like LG entice you on their laundry to connect to the app by adding hidden cycles not on the machine only to be found in the app.

Appliances are becoming smarter than us. I miss the dumb appliances, they lasted longer. -Al

So I tried to fully understand the issue, and I think I got most of it!

1.  It’s a moot point, but the fact he hooked up to hot water baffles me. So odd he even attempted it. Maybe it’s good he’s retired. Probably a nice guy though.
2. It’s ok to run copper to the fridge as most houses are. The copper will hook up to the back of the unit, the solenoid valve. Or some go directly to a union that takes copper to plastic. That is still ok.
3. Most fridges have an internal water filter, so double filtering could cause low water flow.
4. I would disconnect the filter all together let it flow cold right into the unit, and see if it helps.
5. New fridges require a min water pressure to make ice, or you can get the shells you describe. Wondering if it’s just a pressure issue here. Not the fact he did hot at all. Many plastic lines can handle hot water as long as below a certain temp

So while I am trying to fully grasp it, I think if able, you need to test the pressure just before it enters the fridge. If it’s in the 20-40PSI range, it should work. So can he test it before it enters? If it’s good on that end. I would look at replacing the solenoid valve. In case it did hurt or damage it. I still think it’s not the hot water but a pressure issue. I have had newer fridges I delivered in the city with similar issues with no filters. It has been deemed by service to low pressure to make cubes.

Whole house and under-counter units I like the Pelican system. Same for countertop units. I like their system. It’s the same for countertops. But again, if the fridge has a filter, you may want to remove and use their bypass valve. So the double filtering does not affect flow.

I hope this helps, my ADHD kicking today, and I had to read back a few times 🙂