I'm no Starmer fan, but I actually thought he did well, managing an unpredictable but powerful world leader.
It's diplomacy, not grovelling, and he (and King Charles) totally understood the brief here.
I'll try to find the link, but I read an article about how Starmer's team have been building the relationship with Trump since before either of them were even elected, based on the expectation that they both might be.
What's that expression, 'Keep your friends close, your enemies even closer'? There's not point pushing Trump away, that's even more dangerous - they need to work with him, even if that means giving the illusion of pandering to him.
I also read that the No.10 team have been prepping and role-playing out scenarios for this meeting for weeks (if not months). That will have included endless analysis of Trump, his style, his responses to certain things (e.g. royal pomp etc) and also coaching Starmer in body language and dealing with the infamous Trump power handshake. Starmer putting his hand on Trump's should is a countering power move.
At the end of the day it's all about the 'optics' and the headlines. Most people won't bother to watch the whole dull news footage. However the global news media have tended to report Starmer's visit as a success, the global headlines and chosen photos are good and Starmer has emerged as a strong European leader, alongside Macron.
I'm not a Starmer supporter, but I'm relieved by what I saw.