Only Queen I’ve ever known and she has been amazing as a consistent world leader.
It will be mildly disconcerting when she passes as something that was always there is suddenly not.
So I don’t follow the machinations of British royalty: Is Charles not next in line?
Yes, he is - unless he predeceases the Queen, he will be the next King, with Camilla as his Queen Consort. Then William is next, with Katherine as his Queen Consort. Then George, who is still a small child at this stage.
Parliament can alter the order of succession (the Queen cannot) but is extremely unlikely to.
Given the Prince of Wales is already in his 70s, his reign may be short, so many are already looking towards the next generation.