I used to take comfort in the idea that all things pass in time, now not so much. Probably because I realised that includes everyone I love, and myself!
I’ve no great love for the monarchy, but this is certainly the end of an era in British public life and likely in UK international relations - I can’t see the commonwealth nations welcoming King Charles as their new head of state.
And it is weird, there are some things you just never expect to change. I’m hardly a spring chicken, but Queen Elizabeth was not only there my entire life, but Queen far enough into the past before I was born to have interacted with historical figures (like Churchill).
As for people preferring William to his father - I think if you give an inch to the notion that the public should have some choice over their head of state then the idea of a hereditary monarchy starts to look pretty absurd.
Reminds me of when when the rules of succession where changed so that the first-born child would inherit the title (rather than the first-born son). Any attempt to reconcile the monarchy with the concept of equality seems a kinda humourous to me.
Early on, the Swedish king was elected at the Stones of Mora. The Holy Roman Emperor was nominally elected by prince-electors (who most of the time elected a Habsburg).
And even withing a hereditary framework, there are other alternatives to retirement in addition to outright abdication. An elderly monarch could for all intents and purposes retire and a let the crown prince (and I suppose in current British succession order, crown princess) rule, appointing them as a co-ruler.