How can I prevent items from being sent through the portal when thrown?

Hi! I'm new to the forum and this is my first time trying to make a mod for my server. I'm attempting to create a portal with a new dimension that allows players to go to this new dimension and change the mode from survival to creative. I managed to do that, and I also managed to clear the items and set the experience to 0 when returning back. However, during testing, I noticed that throwing items through the portal causes them to end up on the other side, where the world is set to survival mode. How can I prevent the portal from sending items when they are thrown through it? Thanks so much for the support!