That is what I thought until I saw the image below:

https://openstackdocs.safeswisscloud.ch/en/howto/ht-port-forward.html

Hi,

Dnia niedziela, 4 kwietnia 2021 20:43:20 CEST Luke Camilleri pisze:

Hello everyone, I have enable the L3 extension for port-forwarding and
can succesfully port-forward traffic after assigning an additional
floating IP to the project.

I would like to know if it is possible to enable the corresponding
horizon functionality for this extension (port-forwarding) please?

Regards

I'm not Horizon expert so I may be wrong here but I don't think there is 
anything regarding port forwarding support in Horizon currently.