i know this sounds stupid but can you aim your webcam at the tv and my capture card dont want to work with my mega drive (my tv is a CRT)

Yeah, that's fine, as long as the game is clear enough and the audio can be heard.

Note: as the timing is RTA(-TB), playing on PAL will have a time disadvantage.

EDIT: example run that was accepted in S3K being camera pointed at the screen: https://www.speedrun.com/s3k/run/z5j14j5m