I coded a plugin with a custom gui. To open up the gui you do the command /Barbchoose. So I attached that to the portal. It opens up the gui but it closes right away after you tp to the destination specified. Is there a way to remove the destination so it doesnt tp you anywhere. Or maybe it keeps the gui open after the teleport?

What good timing I literally just opened up github and this was here. If you are using portal blocks gui's are always closed because that in vanilla cancels any gui's. You can add a command and it shouldn't say that there isn't a destination but it does move you back (so ive made it think you have warped if there is at least one command, thatll be in the next update)

I have set the trigger block to air, what it does is that it says you have no destination and teleports me back
I don't want it to teleport me anywhere if it is possible I would just like for me to stay in the portal and it opens the gui once or something

It also teleports me out of the portal area so I mostly cannot even walk in but when I am able to it closes the gui right away

Which version are you using? by my understanding what you want is the current behaviour of the latest versions.

This shouldnt happen anymore due to changes. There may be one specific case though it should be fine.