I had this posting in my memory: http://forum.mikrotik.com/t/v6-47rc-testing-is-released/139877/1
And some where I picked up that FWD was an exception.
But then I won’t touch DoH again, even with a long poke. 
It is just a dream for the big firms collecting information come true, people just (want to) don’t see that.
You can argue that are free to choose a more private aware DNS servers but 99% will use Google and Cloudflare in the end…sounds of popping champagne bottles in the background.
That is why I am not happy with Mikrotik implementing it after bring pressured to do that by many post here asking for it. 
Use unbound or Knot resolver through a VPN tunnel. DoH gives you a false security.
This does not mean DoH has not a place. It has a place in countries that don’t allow unchanged DNS usage and VPN. DNS is even sabotaged by returning the wrong root servers IP addresses as Sky UK did or still is doing. Breaking resolving by yourself.
Sadly there are to many people that not aware how we are watched all the time. It is a step back instead of being a step forward in privacy.