Thanks a lot for your valuable reply.
Yes, I’ve just reconfirmed in the other thread that this is the case.
Overall, despite especially silvia’s replies here and there, the whole support from Quectel, although being certainly better than the non-existent one from companies such as ZTE or Xiaomi, appears pretty “half-assed” and mediocre as well with terrible product communication. It is also very odd that some supporters such as mentioned silvia always “conspiratively” send files about supported CA combinations or firmwares directly to users only. Such information should be common knowledge and officially listed somewhere, god damn it!
Sigh, neither do I know how difficult it is in general to change the modem of the Mikrotik router and neither do I understand their portfolio strategy. Their newer model Chateau 5G R16 only has 1 Gbps LAN and AC Wifi despite the used Quectel RG520F-EU (who decides that?) and their 2.5 Gbps model Chateau AX has the outdated RG502Q-EU. 
Now since the RM521F-GL is “end of life” before even having had any of such life, I’m stuck which modem/router to buy if I want more than a SDX62 based one. The Fibocom FM190W-GL (SDX75) also is supposed to be buggy and restricted as of now. I cynically start to wonder what product isn’t alpha or beta state before arriving at the customer. 