If you set up coords in your model, all the arviz plotting functions have a coords argument you can pass a dictionary to. So if in your model’s coords dictionary you have a key-value pair groups:[1, 2, 3, ... , 800], you can pass coords = {'groups':[5, 8, 20]} to only plot data for groups 5, 8, and 20.
There’s an example of this in the docs here if you scroll down a bit.