If i open one port to the internet, is it possible to allow access to it from internet only from a few mac addresses that i specify?

I dont want to open port to everyone.

Filter from inside to the internet is a yes. Filter from the internet is a no, because no MAC address is send with the package.

So MAC is only available on the side of the switch in the Mikrotik and not at the router side/outside.

No, it isn't possible. You can filter by ip address.

So MAC is only available on the side of the switch in the Mikrotik and not at the router side/outside.

There are not sides in thr Mikrotik. They are levels of the protocol stack.