ive used youtube to mp4 converters many times and idk if its illegal, but alot of them are unsafe. the only one i trust is this one but atp its probably alot more ethical to play things safe and just use a fucking screen recorder
It depends you arent gonna get arrested just for having an copy on your computer (as long as its not an illegal video) but depending on copyright you could get struck down by DMCA or the creator if you reupload it anywhere.