X Social Media alleges that Musk’s X confuses potential customers.
X Social Media is suing X, a social media company::Elon Musk’s X is being sued by a Florida company called X Social Media for alleged unfair competition and trademark violations that it says have resulted in lost revenue.
Technically they are not exactly on the same field which could allow using similar trademarks. But on the other hand in this case X's use of X could be reasonably argued to be very confusing for customers and therefore violating X's trademark.