Important: Please understand that the free-form mode is NOT provided by Floating Apps. It's a hidden feature of Android system and Floating Apps only help you to use it. We cannot change how it works nor we can fix its limitations.
The free-form mode is not working on your device
The free-form mode is only available on devices with Android 7 and Android 8. It seems that support for the free-form mode was removed from Android P.
The free-form mode may not work on some devices, because of changes made by its vendor. For example, changes made by Samsung to support their multi-window mode. You may need to flash a custom ROM in order to use the free-form mode on such a device.
Apps are always open in the fullscreen mode
Please verify that free-form mode is correctly activated. Launch Floating Apps and open Float normal apps from the menu to check the state.
It's not possible to start the app in the windowed mode if it is already running or is already loaded into memory. To launch the app into the free-form mode, it has to be launched from a fresh state. Close all apps by swiping them away from recent apps or force close them in phone's settings.
Also, please note that Floating Apps remembers last selected start mode and will use it again for further launches of the same app. Long-press the app to show dialog with options.
Known problem on CyanogenMode / LineageOS
While a device is in the free-form mode, the power button may not work on custom ROMs based on CyanogenMod or LineageOS.
Please test it now as you may lose the ability to wake the device from sleep if the screen times out. Do not use the free-form mode in situations that could possibly lead to this state.
Window sizes are not working on Android 8
Window sizes are not correctly supported on Android 8. This is a limitation of Android platform.
Windowed apps cannot be combined with fullscreen ones
It's not possible to combine maximized apps with windowed ones. This is a limitation of Android platform.
Apps cannot be restored to the windowed mode.
Apps that are maximized cannot be restored to the windowed mode. This is a limitation of Android platform. On some Android versions, it's possible to restore the windowed mode from recent apps.
If the free-form mode is still not working for you, please visit the page with information about limitations and possible issues.