The unspoken truth about this Starmershit is that it's a total break from tradition. To see this you have to understand the oddities of UK law on this
1. The monarch always retains authority to remove a prime minister, and customarily does this when a PM becomes too politically weak to advance the crown's agenda.
2. Typically they don't wait too long. Queen Elizabeth didn't waste much time getting rid of BoJo or any of the others, really. Under her reign, Starmer would have been gone months ago
3. The holdup is that, as a legal technicality, the monarch does not actually fire the outgoing PM, but instead selects a replacement. In other words, Rishi Sunak had to be chosen (behind closed doors) to be PM before BoJo could be forced out.
4. The PM can also submit his resignation to the king, BUT in order to "accept" the PM's resignation, the king is again expected to have a replacement lined up
That's where Charles fell apart. He was too lazy or incompetent to locate a successor. He let Starmer twist in the wind for six months, and even when Starmer announced his resignation it took several more weeks for Charles to "accept" it. Look at the absurdity of Starmer saying "I'm out" and then staying on the job like that, while also being the least popular PM in UK history