Can I enable 'Dynamic Endpoint' on the server node?

no, it is not possible

So I suppose the notion of servers behind dynamic dns is impossible for now

no, it is possible but the recommendation is that netmaker servers have a static public ip

well the problem then is this: when my public ip is updated, while the clients are connected (mqtt and api) the server's public wireguard ip is not

too early in the morning, I mis-read your question and thought your were asking if you can set dynamic port on server (which will not work satisfactorily).. Toggling the dynamic endpoint on the server node should work fine

I had the impression that the server needs a static IP. its no longer the case?

it works better with a static ip, but netclient connects to the the api/mq via a FQDN so as long as your dns entries are propogated quickly netmaker comms between netclients/netmaker servers will work

well, If you go to the dashboard and try to toggle the dynamic endpoint on the server node, save, and go into nodes and check server node again it gets auto-disabled

yes, you are correct. my bad

I suppose its a bug?

not necessarily .... not sure how a dynamic endpoint on the server would work ... I think it is disabled for a reason