Sorry, I've only just seen this for some reason. It came as a bit of a shock to everyone in the UK, which given her age is a bit surprising - until Prince Philip died in 2021 I think everyone just assumed she'd make it to 100+, even after that a lot of people seemed to be a bit shaken when it actually happened.
The transition to Charles seems to be going fairly smoothly - still haven't seen any stamps or coins with his face yet. They changed the definitive stamps (the ones used for most letters) last year to add bar codes and must have had huge stocks printed when she died, so that'll be a while. Not sure about notes and coins, I think that they were coming round to the next release of bank notes in the next year or two. There have been some 50p coins already but that was a short run which must have all been grabbed by collectors, I've never seen one.
I'll be honest - it doesn't impact me much. Although I live in London I've never even seen any of them in the flesh, and I'm a bit of a cynic about the way Royal news and rumours seem to be trotted out whenever the government needs a distracting news story. I think people are still waiting to see how Charles and co. work out, but I doubt there will be any sudden change - there's way too much inertia, and political pressure to keep things exactly as they are.