question to all - are you connecting your 4k x directly into your mac, or through a hub?
I'm getting the exact same issue, and of course the first few question the trouble shooting of Elgato, or the hub manufacturer asks is can you bypass the hub, or go direct into the Mac.
I'm using a CalDigit T4, and I'm now going to test the capture card using Meld to see if this is an OBS specific issue.
I'd like to know if anyone has a solution to this issue that doesn't involved running scripts, and also the method posted
here doesn't work for me - I've tried legacy, I've tried capture card device, and just standard video capture device.
In fact because I'm plugin and un-plugin the hub with the 4k x into my MacBook, using capture card device works best for remembering the source when I plug everything back in, as where the others forget, and each time I need to set the source to default and re-selet the card.