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It doesn't work at all anymore. I tested everything including the stacked sector things (which still work), Also, Hexen and UDMF formats (not the problem). I downloaded a tutorial map and it was broken. Sorry, I can't supply a demo right now since I'm posting with my phone (Internet is out, don't ask).

If you can't upload a test file, please describe the exact setup you're trying to do (in as much detail as you can muster). Also include the version of GZDoom you're using, and make sure to test with a fresh .ini config. Portals are notoriously finnicky to set up, and saying "it doesn't work" gives us nothing useful.

Here are two simple maps. One of them is from a ZDoom tutorial website. The goal was to get any portal to work whatsoever and it failed.

Maybe the setup changed from ZDoom to GZDoom?
Here a map I've tried with 2 setups : Interactive portal and Link to portal with same tag and both works. (just change the types)
The other types show a black square but I think they need to be configured in a different way

By the way I followed this tutorial : https://www.youtube.com/watch?v=jBXxVc1X8bE and I've noticed some differences with your maps.

oh I am using GZD 4.14 with Vulkan rendering

Your map works on my computer. Just by changing the type to interactive, I was able to fall through the hole in the floor! I still don't know why my map doesn't work though. I will have to look into this more.

Have a look at the video I linked and at my map on UDB.

The linedefs on the map is not a 64 unit long but two 32 with specific settings.

Your map has a 64 unit long linedefs which I think it's the problem.

Oh and check the heights of the sectors. The floor of one sector and the ceiling of other must be the same height.

I got an interactive portal going in my level (finally!). It appears that using a one line per sector approach just isn't supported. I tried a bunch of older GZDoom versions and none work with the one line approach. I used 64 length lines and that doesn't seem to be what the problem was. Of course this isn't mentioned on the wiki anywhere which is a bit misleading and was what got me stuck.