I was part of a team researching MS at a university a while ago. It truly is an endlessly fascinating disease. Most evidence currently points to MS being caused by a combination of Epstein-Barr infection and genetic factors [0,1]. It is hypothesized that Epstein-Barr triggers autoimmunity which results in the prototypical demyelination [2].

[0]: https://www.science.org/doi/10.1126/science.abj8222

[1]: https://www.pnas.org/doi/10.1073/pnas.2424986122

[2]: https://www.nature.com/articles/s41586-022-04432-7