Matrix is a federated protocol, so it depends on what server you use (including self-hosting your own). Not using it because a server has a lot of furry porn rooms would be like not using email because hotmail has furry porn.

For what it's worth, I've self-hosted a matrix server for years for my family and friends, have participated in a reasonable number of rooms on the flagship matrix.org server, and have never run into any furry porn.

Don't go on the internet.

a friend wants to know what server this was...