Looking at the Govern / Trade menu it shows me as having -2/3 trade routes available. I have 1 trade route of my own and other civilizations started trading with me, for a total of 4 trade routes.
Also, I reported this earlier (2 versions ago) but it still isn't fixed. When I purchase a freighter from another civilization, it should ask me what should be its home world because I cannot use it as a freighter. When I attempt to create a trade route it will tell me it doesn't have a home world.
If adding a popup to ask the player what the new home world is going to be, a quick fix would be to pick one of my home worlds at random. It's a quick fix but will make freighters useable. (The upgrade menu should ask me this, also if the home planet of the freighter does not belong to me).
Secondly, if my planet flips, and I have a trade route linking it to another civ, the game should also ask me what the new home world is going to be for my trade route, so that the freighter can be re-used.