The RF do it all the time. And release pics themselves.
The only time I can think of where a member of the Royal Family has visited someone’s home like this was when William visited Deborah James at home to present her with her damehood shortly before her death. Which was (a) not a surprise - as she explained, it was arranged in advance, giving them time to clean and tidy; (b) was something he would have done anyway since he hands out honours at investiture ceremonies, but she was too ill to make one; and (c) he is patron of the Royal Marsden - a charity Deborah of which was a passionate supporter. Also, it was Deborah and not the Palace who publicised the event and released her pictures - I presume if she had wanted to keep the photos of the visit private, she absolutely could have.
Otherwise Royals have turned up at pre-arranged NHS charity functions to thank the attendees, and have taken part in already happening charity events (William turning up to publicise a mother’s charity walk to raise money for teenage mental health, leading to a surge in donations, for example). Again, those events are supporting the charities and thanking others, not themselves.