There isn't a category in LiveSplit because it's an Individual Level run, so all you'd need to do is just stop the timer once you get to Level 100 (don't worry about being super accurate about stopping the timer, we'll retime it for you to make sure you have an accurate time on the leaderboard)

As for sharing the video, once you've recorded it (via a recording tool like OBS for example) you'll need to upload it to an external video hosting site (like YouTube) and then when you submit a run you should copy the link to your video and submit that with your run.

Hello, for the Worlds 1-8 Boss Marathon category, is it required to defeat every level with boss enemy (such as 2-9 and 2-11), or just the boss at the end of each world?