To be honest it completely sounds like you have no idea I am talking about and you are trying to give me advice anyway.
Repeating, I am trying to ask if it is possible to use the "Full screen projector (source)" FEATURE that OBS has that has it's own Independent FPS settings through the "Video Capture Device" source to view the capture card at 60FPS while outputting the lesser 30 FPS. It seems like it is not possible because changing the output FPS brings down the "Video Capture Device" FPS to the outputs maximum.
I'm asking because this is very possible already if I use a nasty work around of instead using OBS video capture I just window capture Elgato's own preview screen. ....As well as this pretty much being possible on anything running on your own PC, when you stream a game you are playing at 60FPS and output 30 it doesn't suddenly drop your game to 30FPS while you are playing now does it?
Here's another person asking pretty much the exact thing in the past I found just now that never got a answer if you still don't understand.
https://obsproject.com/forum/threads/preview-capture-device-at-60-fps-stream-at-30-fps.54934/
Edit: In fact I can also do this by opening up 2 OBS, have one capture video device with the "60FPS" output, send the projector source, open a second OBS have it window capture the projector source and set it to "30FPS" output and there we go, I can play at 60FPS while streaming at 30FPS, but you understand how stupid this workaround is right? It's exactly why I'm asking if/how is it possible to do in OBS alone and if it's not possible guess that would just be a feature request.