The problem is that in terms of things that the govt might want to achieve in regulation of social media, and AI, Musk is an important player. It would be better to have a working if not sycophantic relationship with him. It's not Starmer's fault thar Musk has decided to become an 'edgelord' as ad_O highlights, but it's not ideal.
The movement of IT players behind Trump is difficult to evaluate in terms of effect till after the US election but it does make me doubt their intentions when they talk about wanting regulation on AI.
Given the move away from twitter/x Musk is becoming an increasingly less significant player. And it wouldn't surprise me if that decline continues as people pivot to other platforms. There are plenty of UK organisations that has taken a decision to move off twitter/x and I imagine there will be similar movements in other countries.
But on regulation, I think governments, singly and in collaboration need to determine the appropriate scope and levels for regulation. While companies will need to comply and, quite reasonably will need to be formally consulted with particularly on the basis of unintended consequences, regulation must not be in hock to the media companies. I can think of many examples across a range of sectors where there have been major changes to regulation that significantly impacts the work of that sector. In most cases this has been simply imposed, at best there has been limited consultation. In no case has the regulation been brought in only with the explicit consent of the sector, such that they have an effective veto.
If regulation is brought in and Musk doesn't like it - tough.