I already saw the post Synology RT1900ac supported? which says the Synology RT1900ac is not supported yet but the post is already a bit older.
So my question is, could it been done without greater work?
with 4.x gone... it's less doable...
mr2200ac is ipq4x, much better board... ( but pricey in comparison to competitors )
the short answer is it's not worth it... bolt an SBC to the top and use OEM...
Sad but thank you @anon50098793 for your answer. Finally I will sell the router.