Conservative PM Cameron resigned, and paved the way for Teresa May- 2016-2019, not elected by the public. She was internally deposed, followed by Boris Johnston, 2019 to 2022. He was deposed followed by Teresa May ( not elected by the public and lasted 5 weeks) the Rishi Sunak ( not elected by the public and he called an early election) 2022-2024.
That wreaked havoc on the Conservative Party, the public's trust and they lost the 2024 General Election with one of the lowest, if not the lowest Conservative vote share in history. Clearly such PM changes are not good for the country and not liked by the general public.
There can be little doubt that Starmer made a mistake (in hindsight/bad judgement call) appointing Peter M, for which he has apologised. It has not be proved he lied or mis led Parliament, to my knowledge. Starmer deciding to sack Olly Robbins for his failing/mistakes, as perceived by Starmer that is, was the wrong call. Also it does not sit well that Starmer believes he should "fight on" and he gives mixed messages over his perceptions about accountability. That is why was Olly Robbins sacked for his perceived mistakes/failings- but not Starmer himself?
Having said all that, the amount of time and media coverage devoted to this sad state of affairs, in context of cost of living crisis, geopolitical world events and wars and consequent impact on the price of oil and diplomatic relationships- seems somewhat disproportionate.
Further, Peter M's appointment did not cost the public £billions( eg as in the Conservative Government's PPE "VIP' lane fiasco, Liz Truss's market havoc that added £100s pounds per month to many paying their mortgages, Referendum that lead to Brexit decision and its consequent high adverse outcomes such that well over half the population feel we should never have voted to leave). Peter M's appointment did not lead to any controversy, problems, adverse diplomatic relationship outcomes when he was in post during his term as US Ambassador. Any recent US/UK relationship decline, after PM was sacked- has been wreaked by Trump, not Peter M and not only on the UK.