In AGOL Map viewer, group layers require both the parent group and the individual sublayer to be turned on for the layer to draw.
However, when a user turns on a sublayer within a group, the parent group layer does not automatically become visible. This can create confusion especially for less technical users because the sublayer appears to be enabled but nothing draws on the map. We have run into this issue a lot when sharing apps with non-GIS staff where they assume the layer is broken.
When a sublayer within a group is turned on, the parent group layer should automatically be set to visible. This behavior should apply consistently across web maps and apps that consume web maps like Experience Builder and Instant Apps.
I have attached an example to show what I mean. Selecting Tree Canopy should automatically turn on the Conservation group.

Thanks for reading and hopefully this can be a feature in the future!