Hello Anonymous - it is the same for me. The reason for the difference appears to be because a patch has been released to the PBI service, but the Desktop application is awaiting the next release (latest version is still Dec 2021).
v-yingjl - can the above be confirmed? Secondly, I would like to clarify that if the bookmark navigator is completely deselected because another bookmark (outside of that group of bookmarks) is selected, then this (whilst an improvement) is still not an acceptable solution. An acceptable solution is to have the bookmark navigator persistently showing the last selected bookmark (from the bookmark group the navigator is referring to) until another bookmark within that bookmark group is selected. This should persist for any number of other bookmarks (outside of the bookmark group the navigator is referring to) that are selected. Please confirm.
PBI Desktop screenshot with reported bug
PBI service screenshot with suspected patch (improved but not acceptable solution)
PBI Desktop with requested fix (acceptable solution)