The Crown will have no impact wahtsoever, IMO, on any public reaction that C&C may face, should they attend a service at a local Gloucestershire church for a Christmas service. Thankfully, life on the ground is still not akin to that on social media!
Yes, I'm not really sure I can see the locals lining up to boo them as they go to church on Christmas Day and are many people going to travel to rural Gloucestershire to yell insults and picket them on the off chance they're going to an in person service at one of the churches?
I don't think Republic protest the walk in normal years do they?
That said, taking a look at St Mary's Tetbury website, they're still doing Zoom services and haven't yet finalised anything for Christmas publicly. It's likely places will be extremely limited for in person worship if it goes ahead and you have to book in advance. So I don't know if we'll see them walk to anywhere on Christmas Day, although Charles might participate in the online versions of Canterbury's services again.