Apparent MarvinSketch is freezing under Big Sur, This problem is caused by a change in tab behavior in Big Sur. Newly opened dialogs are handled as tabs by default now.  The issue can be solved by changing the tab preferences of the system.

Details are here https://chemaxon.freshdesk.com/support/solutions/articles/43000613604-marvinsketch-freezes-on-macos-big-sur.

There are more details of Scientific Applications Under Big Sur here.