𝕏 is actually a Unicode symbol, so musk can’t trademark it
That’s not true, it absolutely can be a trademark. You might be thinking of copyright - he can’t copyright the current 𝕏 logo.
The rights you’d get from each protection are different and a sensible business probably would want both. Trademark protection would prevent another tech company trading as 𝕏; copyright protection for the logo would let you set terms on how it is used.