Yes, Mountune is not warranty friendly to the MK8 as it was for the Mk7.
This is covered on the forum in a few places mate. Probably best we avoid another huge thread on this but:
1) there are people who have m225/m235 and have needed warranty work (not for faults seemingly caused by the Mountune kit it would appear) who have had their warranty work completed without pushback from Ford.
2) Mountune are still a hugely reputable company who, despite their price and lack or product availability at times, have an excellent record with reliability and product quality. Even other tuners don't have chequered histories with the mk7 and mk8 remaps when it comes to the maps causing the cars to break/fail/have issues
3) Despite the above, it's still on you if you buy a car, mod it with Mountune or any other tuner, and then experience issues. Ford ultimately could reject a claim, as they're entitled to, despite the recent reports of warranty work being carried out on modified vehicles.