you need to make the settings.
if you have follow the instruktions and installed all correct you need to tell what drive in what mode (resolution/fps/colorrange) the source operate.
if the cam sends a signal to the camlink that he not support you will have no success
so first check out if the cam runs a from camlink supported mode
then check if camlink correct install and setup
then add it in OBS and set the same settings the cam and camlink Operate at
you need to configure the camlink with the " Game Capture" software from elgato the set the settings for the operation mode
there is a view thinks that can go wrong if you not follow the instructions
a short google search shows massive tutorials to correct setup camlink4k with OBS and it requirements to get it to work