Sure!

https://ffmpeg.org/

restream .io has a converter. Or veed. io (watermarked it you don't pay for it). Handbrake is open source. Seven Converter from Github might do the job too.

HandBrake

https://handbrake.fr/

$: ffmpeg -i video.webm output.mp4

ffmpeg via VLC player.

Definitely ffmpeg if you're comforable using the CLI. There is a good chance any tool you're going to find is using ffmpeg under the hood. Handbrake is a good example and would be my go-to choice for a GUI.

ffmpeg