I realise this is probably a really silly question…but im very much struggling to see the difference between a panel iFrame and a panel custom?
is it that daft a question?!
I’ll take a stab here. My understanding and usage of the Panel iFrame is for linking to an external website outside of Home Assistant to load in the HA window. For example, I have a sprinkler system on my internal network that uses http://192.168.1.x/sprinkler. I added a Panel iFrame component and added that URL so from my Home Assistant home page I have a clean panel link on the left panel that takes me to the sprinkler administration page in an iframe. I have the same for my connection to NodeRed.
My understanding of Panel Custom is if you want to host a full custom HTML page on the Home Assistant instance. More than linking to an external page you are loading in an iFrame, it could be be a full customized view of Home Assistant items with ability to control them.
I’m still a HA noob though but that is my brief understanding of the two components.