We have this layer in a sde that is produced in enterprise portal. I recently have been converting from Web App Builder to Experience Builder and changing all maps from classic to Web map viewer. All of sudden one of our layers keep showing this error. and everything is greyed out on the right hand side. You can turn the layer on and off no issues there as to seeing it correctly on the map.
NOTE: The layer is in multiple maps and behaving the same in all the different maps. Also, in the sde no trouble editing this layer and seems to be no issues there.
Screenshots for reference.
data is inaccessible error
greyed out options even though the layer is selected.