Have been looking for a way that I can have new topics automatically added into or. through my Mastodon account. Haven’t seen much except through Zapier and that involves a seperate (4th party) service as well.

Is there another way to go about this?

Zapier would be the direction I would be going in, if I was doing this myself. Your only other alternative really would be to employ a 3rd party developer to create a direct integration with this