This thread on X is a summary of the lawsuit:

Tracy Beanz on X: “????THREAD: Elon Musk’s X Corp is suing Media Matters. Here is an analysis of this concise complaint. I will be reporting on this case as it progresses. This will be the main thread, so please bookmark if interested. You can also find it on my Highlights page. LINK:… https://t.co/lbmGUGSGJp” / X (twitter.com)

The lawsuit alleges that Media Matters created a highly tuned account, designed specifically to ultimately put inflammatory content adjacent to key advertisers. Media Matters then, per X, repeatedly refreshed the account’s feed until eventually seeing an ad next to the content. In most cases, according to X’s own data, this ad pairing was seen solely by the individual at Media Matters who was working to create this pairing. Media Matters then took screen snapshots and used those to persuade major advertisers to pull advertising from Twitter.

The goal of Media Matters is to shut down Twitter/X. Their past writings show they do not like Elon Musk or his removal of intensive censorship from X. You can learn more about Media Matters and their history here: Media Matters for America – Wikipedia

And also read about Media Matter’s President – a former executive staff member of the Democratic National Committee – Angelo Carusone – Wikipedia

He has long advocated the advertisers pull out of Twitter once Twitter was no longer conducting widespread censorship operations.