Regarding Proportional Representation I think Labour and Lib Dems have said yes to it. It’s been long over due in my eyes. As for Reform UK. The only exist to ruin the Tory vote. There after, nothing. Now Farage has joined and become leader as Agent Provocateur.
I’m not sure about others in the Labour Party but Kier Starmer is definitely against Proportional Representation.
Personally, I too am very against the idea as all it does (In my opinion) is result in very messy coalitions that never actually get anything done and who end up blaming each other whenever anything goes badly.