DNS menu is locked after v6.4 update
Workaround new:
- Just close menu and reopen them.

Workaround (old):
- new terminal
- /ip dns set servers=8.8.8.8,8.8.4.4
- Close DNS menu
- Open DNS menu, ip - DNS
- Now dns menu is unlock

DNS menu is locked after v6.4 update
Workaround new:
Workaround (old):

It is not just the DNS menu … more like just about every other menu too.
Just opening again will let you make changes.
I can confirm too. When first time you open any settings - there are inactive, but open second time - options are active.