Discord has a weird and confusing definition of “server”. The equivalent in Matrix would be “spaces” but they are not very commonly used (and I’m not sure there is a public list). Instead Matrix is most often used with individual rooms.
Due to the distributed nature of Matrix it is actually impossible to create a complete list of public rooms. However, one probably fairly complete list can be found at view.matrix.org. Most clients have room search built-in, so you would rarely need that list