Each room has a number of attributes to generate different layouts. You can change those values individually for each room in Administration > Rooms

key	default	meaning	availabe since OpenMeetings version
hideTopBar	false	Hide the top bar with the menus and exit button	2.x
hideChat	false	Hide the chat tab and use space for whiteboard	2.x
hideActivitiesAndActions	false	Hide the activities window with the notofications aber user activities	2.x
hideFilesExplorer	false	Hide the file explorer	2.x
hideActionsMenu	false	Hide the menu with the actions	2.x
hideScreenSharing	false	Hide the button to start screensharing/recording	2.x
hideWhiteboard	false	Hide the whiteboard, if this option is true, the videos will be in the area of the whiteboard	2.x
showMicrophoneStatus	false	Show the current status of the microphone (off/on) on the bottom of each video view	2.x