First, it works perfectly using firefox and older (11.x) version of Safari, thus could be related to Monterey updates..
It seems to be related with some Z-order issue, when all panes are activated pulldown menus show up below both upper panes (editor in my case). But as soon as I zoom in one of these panes , menus show up properly. That's odd, anyone having the same issue ? I have checked and besides Mendeley I have no other extensions running... any tips appreciated.