I have a microtik with 3 APs connected and my inet provider router. Ports are added to a bridge.
I want to add a new AP, but it doesn’t get any connection from the router. I tested the cable and it is fine. When I went into the bridge in winbox I notice that all ports other than the already existing connections are listed as disabled. How do I change a port from disabled port to designated port? Is this why my new AP gets no connection?

Ports which are not in use on bridge, are labelled “disabled”.
Once you connect a device to that port, it will move to another state.
You can also disable those ports manually but then they would be greyed out, which is not what I see on your screenshot.
If you connect your computer to one of those ports, does it work then ?
Other possibility:
The access points you are adding, are they functioning ? They do not require power over ethernet ?