2019 Ecosport charging stystem behavior

I 'm really sorry you have had so many problems.
Back in the day, battery, alternator and even old-style generators were easy to diagnose. These days with certain electronics drawing power even when the car is not even running...well that's beyond my knowledge.
I do know alternators rarely fail. If it's not charging properly, it could be a loose belt, a loose connection, or some kind of computer fault.
Also, and as you said, the average life span of a battery is roughly 5 years.
I have a cheap battery/alternator tester. Sometimes it says battery good, other times it says battery good but needs charging.
Since the battery is approaching five years, I suspect its more that than a bad alternator.
Fortunately, in my hometown we have an excellent battery shop. They will test your whole system with far more sophisticated equipment than what you might buy on Amazon for free.
If you have similar battery shop....go there and see what they say. To be clear, I'm not talking about AutoZone or similar national brands. They may be fine, but I don't trust them.
It's a shame that what was once simple things to diagnose are now so complicated that you don't know what to believe.
Sorry for the last part...I'll get off my soapbox now...lol

Follow up to my Original post. My Midtronics 300 had already noticed the OEM battery was down a little on capacity, so I was not too upset they let it sulphate while the engine was being replaced. Plus there was some drama involved. They were "having trouble" starting the new engine. Thought the ignition switch was defective, replaced it, the key cylinder, the PATS antenna module, then decided it was a range sensor in the transmission, then after replacing that, it was the floor shifter assembly that needed to be replaced, and then, they found "a bunch of wires under the dash that were cut and out of place". Total mystery on the wiring issue. They had replaced the long block assembly the turbo and the water pump, but the alternator is the original one. I put in a new (dated 3/23) German made H6 AGM battery and did the in vehicle reset procedure for the Battery Management System. Still charging at 12.6VDC. So I connected up Forscan, and there were at least 50 DTCs present from the battery being dead and needing a jump start. My fault for not checking that. I cleared the DTCs and let Forscan do a BMS reset. And now when I first start up the Engine it will charge at 14.3VDC, then about 10 miles into the trip it will drop back to about 13.4VDC, but coasting to a stop or sitting in traffic it will be at 12.6VDC, enough to keep the battery from discharging but just so. I guess that saves gas? I don't know the theory of operation for the BMS. But I don't remember this behavior in the past. Was hoping someone knows if this is normal...

Marc