is this the nest of a dormouse or a bird
No interactions present.
And tricky to get a good idea of size.
It could be either, I think: perhaps someone else with more experience can pronounce on it. I did some work on dormice years ago, but that was focussed around putting up nest-boxes for them!
Difficult to judge from the image, without any size of scale, as Amadan says. It looks like this nest is cup-shaped & mossy. If this is the case then it is most likely a bird nest.
Montgomeryshire mammal recorder and generalist
Lat/Lng: 51.0524, 0.4575
OS grid ref: TQ723309