Doesn't matter i have an rb5009upr and i still had "dns, memory DoH server response not OK: 0" logs, like to the point where it started ignoring the logs and at some point there was 2 logs on my router, that warning and my winbox logins...
Shared it with support, they said its not a mikrotik issue that its my certificates, i imported all the certs, activated all their certs and imported the Quad9 certs. Showed them that and the router logs again (it was the same) then i just got told that its an issue with Quad9 DoH.
Later i saw development 7.26 patchnotes and right after my support ticket there was one line that got my attention.
I honestly don't care to spend more time or troubleshoot it further, theres no point theres something wrong with either mikrotik way of handling it or Quad9, dont use their DoH. Simple.