So I have a few different (possibly related?) issues with theater view and/or display view on Mediacenter for Linux specifically (these issues don't exist in Windows to my knowledge). Some of them are repeatable bugs, others are more temperamental, let me know if you want me to split out any of these into separate threads. I've experienced all of these running MC 29 for Linux with build 29.0.20 on Debian.
1) If you open MC in standard view and press F11 (which I've mapped to the green remote button to get correct behavior on Linux) MC switches to theater view as expected. However, if you then press F11 a second time immediately, MC presents as a blank white window and any further presses of F11 or other attempts at navigation are ignored. I can usually recover by hitting Ctrl-1 to switch back to standard view, but obviously getting to a blank white state that doesn't respond to remote control input isn't ideal. By contrast, if I press F11 once to switch to theater view and then navigate down into the theater view menus, a second press of F11 will correctly return me to the top level theater view menu and further presses of F11 will correctly toggle back and forth between menu locations. The issue only seems to predictably happen when someone accidentally presses F11 when in the top menu at first open before navigating. I can reproduce this on several machines including two running Debian 11 (on with Gnome, one with Xfce4). I'm using Noire as my theme, but see the same results in Obsidian.
2) Less predictably, theater view sometimes winds up in a white screen state for unpredictable reasons. For example, if I set MC to start up in theater view it will often start in a white screened state. This is new(ish) behavior in that this wasn't happening in early MC 29 builds, although it only happens about 75% of the time. This only seems to happen on Gnome, but not on XFCE (I can reproduce it using either the Xorg backend or the wayland backend). Also sometimes a lot of fast "back and forth" seeking in display view can trigger a white screen (not sure if related).
3) MC behaves a little strangely in setting itself to fullscreen for display view or theater view (this is a longstanding issue for me that's been around in some form since MC27 at least). This presents differently in different desktop environments. As an example, in XFCE if there's a panel somewhere on the screen, switching MC into theater view won't set itself to full screen: it will only fill the space above or below the panel, so the only way to get actual full screen is to set the panel to hide itself. On the other hand, in Gnome, while MC will correctly full-screen itself on the transition to display view or theater view, but when I switch back to standard view the standard view window will be fullscreen obscuring the top bar. Window resizing also stops working correctly at that point (the maximize button no longer responds and key shortcuts cease working), so the only way to get a normal window back is to close and restart. Not a huge issue, but something I thought it was worth reporting.
Let me know if I can provide any more info.