There's a staff of secretaries dealing with all the Royal correspondence. My Mum's friend was one of them and was sometimes called out of retirement to help out at busy times like Christmas or anniversaries and other royal events which require lots of letters/cards/invitations/thank yous etc.
34 year old assisted euthanasia
Harry and Meghan ‘royal’ tour of Nigeria.
Forgetting where you left your keys dies not mean you are “losing it”