Make the changes suggested. You will also need to be certain that the web sites A record is entered on the MiaB Custom DNS page in the admin area.
Do not make the change suggested. Instead move the DNS records needed for MiaB for that domain to Digital Ocean by copying the information found on the MiaB External DNS page in the admin area.
Now - due to the nature of how MiaB is configured and due to the fact that the original intent was solely to focus on email I am going to HIGHLY recommend that the name servers for domains which have active websites hosted ELSEWHERE (not on the MiaB server - which should be MOST websites) be run elsewhere. The reason for this is that the MiaB server is a single point of failure as the default configuration does not have a secondary DNS server. If the MiaB server goes down you will not have a website that is accessible either because you have no DNS service as it is down. If you are running email only on a domain, this is not a huge issue, but if you have external websites then this could be a major issue.
Alento, nice answer. There is also something really nice running on Docker Containers.
But Anikasing, I see a lot of questions within a very short moment of time. Just try MiaB. If you like it, use it. If you want payed support, probably Alento, Murgary or other users of this forum can provide that.
A little bit more reading/experimenting would be nice.