@m_magalhaes Thanks for the confirmation.
I have meanwhile found that while the API doesn't cover the OM window states, you can still call CallCommand and IsCommandChecked on the functions.
c4d.CallCommand(100004762) # Show Search Bar
c4d.CallCommand(100004719) # Show Path Bar
c4d.CallCommand(100004746) # Show Filter
They only address the last used OM though; it doesn't seem to be possible to target a specific OM (like it is possible with the Open/Close flags which are stored as NBITs). And of course it doesn't tell me anything about the current visibility of an object in the OM.
If the developers will think about commands to cover the filter/search/root conditions, they may want to go one step back and think about a more general concept to handle the multi-copy windows (Object Manager, Attribute Manager, Timeline) in some way that allows me to ask what was the last window, the active window, a window by index.