I used to be a big fan of PR but I am not any more. I think it's a really good thing that FPTP forces all major parties to seek the compromises of occupying the middle ground and appealing to as many as possible and fringe extremist parties generally don't get a chance unless by coincidence a particular constituency gets motivated and captured by a specific extreme ideology.
The biggest problems are in having an effective functional government. A coalition between 2 mainstreme parties is manageable. Under PR you'd have a minimum of 3 parties in every coalition that manages to cobble together a functioning majority, and many more smaller parties would need to work together to form an effective opposition (and an effective opposition is important to hold a government to account and provide a coherent challenge to theur narrative). There would be 16 different parties (based on 2024 results) with at least 1 mp, nine of which have at least 5. An opposition coalition would need to beat out a compromise between 4-6 parties in order to oppose a bad legislative idea.
There could be no clear way to hold any government to account on its manifesto promises because every coalition would need to seek a compromise between their incompatible manifesto promises. Doing this is what annihilated the lib dems in 2015 - they promised in the 2010 election no student fees because they had plans for a graduate tax. They negotiated a reasonable compromise where there were fees which if you understood the maths would be adninistered in such a way as to ve indistinguishable from a situation of no fees but a graduate tax for most people. This is the nature of coalitions and parties would stop having manifestos of carefully interlocking and coherent policies for how they would tax here in order to spend there because all such plans would always be abandoned anyway during the quest for compromise. Instead we would be expected to elect parties based on woolly and unaccountable priorities and principles any of which might have to be sacrificed during coalition negotiations.
Countries with coalition led governments often spend years in a chaos limbo where the parties are spending all their energy squabbling about how to form a coalition that they don't do any actual governing - don't pass any legislation or make any much-needed reforms
UK-wide PR would annihilate regionally-focused parties in the 3 devolved nations and would be also be totally unworkable for independent parties - independent candidates won 2.0% of the vote so theoretically should have 13 seats but how would you choose which 13 from the hundreds who stood? There would be no rational way.
Under any list-based PR we would never again have a "portillo moment" of a cabinet member losing their seat - each party would ensure their big names were at the top of the list and there would be no way for voters to rid themselves of an individual who lost the confidence of the voters.
FPTP isn't great and there's room for improvement but PR would cause more problems than it solves.
A hybrid system with a mix of directly-elected and PR-allocated members calculated on a regional basis would be notionally fairer and could be carefully structured to avoid some of these problems but every tweak made away from simple PR or simple FPTP introduces conditions so complex to describe and administer that the electorate would hate it