Disclaimer: IANAL, and this is not legal advice.

Trademark infringement is a civil matter. If you called your company Twitter, it would be up to the current holder(s) to issue a C&D, lawsuit, etc. If they do not protect their trademark as such, they can lose it. Which would be a very interesting scenario- Musk is very adamant on pushing his favorite letter. This would require them to state in legal filings that they still want and use the name Twitter. Undoubtedly this would hurt Musk’s ego, and it’s possible that he would force the matter to be dropped.

Also, trademarked names are not absolute. You can use them in contexts where consumers are unlikely to confuse the two. Apple Computer famously had to distance themselves from Apple Records. There’s a Dell aluminum siding company near me. There’s a Hershey ice cream brand that’s unrelated to the famous chocolate company. While it’s harder to make the claim when the word is unique nonsense, you could probably get away with a name like Twitter Landscaping.