An HDMI Capture Card increases the amount of data an external camera can send to a computer during a recording session. When using an External DSLR or Mirrorless Camera, an HDMI capture card allows you to record with a higher resolution than a USB otherwise would.
Among Riverside creators, a commonly used capture card is the Elgato Cam Link.
Cam Link 4K
Check your external camera's compatibility and its maximum resolution on Elgato's website.