Depends on the quality. YouTube 4k is about 25mbit/s, so that's 3-4 4k YouTube videos playing at the same time on a 100Mb/s connection.

4k Blu-Rays OTOH can be about 50GB or larger even. You wouldn't ordinarily stream that but you could stream one or two blu-rays with a 100Mb/s connection.

100Mbit/s is plenty for current use-cases.