I never mentioned that the SD cards "in trouble" are MicroSD cards with 64GB Sandisk ExtremePlus V30 XC 1 class3 A1, and I used the Slot1 in the A7III
I used Disk Utility to format to ExFat, put the card in the camera and formated, put it to record and the files ended up 4,19GB each again. Please see Pic-1 where it shows a screenshot from Finder. Then I checked the card with Disk Utility and it showed "No NAME" and that it was MS-DOS.. See the Pic-2 attached.
My conclusion is that the camera formated the card to MS-DOS for some reason thus chopping files into 4,19GB each.
I took the Micro SD out again and formated it to ExFat in Disk Utility, put it back in the camera. It didn't ask to format the card, only let the camera fix the Database, it took 5-6 seconds. Then I recorded a long video resulting in one big MOV file.
When I use the full sized Sandisk SD Extreme Pro 64GB 170Mb/s XC 1 V30 card, everything is fine. Formated in Disk Utility, the put in camera, formated, and it's not chopping the files at all, see the Pic-3 attached.
The crazy thing is that I have two of these MicroSD cards, completely identical, bought on same occasion . One card is being formated the right way in camera (to exFat) and the other one into MS-DOS. Tested this 3-4 times, always the same card.
Now I know (I marked the card) which shouldn't be formated in the camera and I won't have troubles any more, but it's maybe good to know for others, it's either the card or inconsistent behaviour of the Sony A7III formating sequence. Is it firmware issue or what, I wouldn't know.