Talking about MIUI 13, they seem to be intentionally locking down features too, causing bugs while doing so.
I have a POCO F3 and I used to be able to split screen while having a floating app and an app specific "custom" floating window (eg: vlc, youtube, newpipe, maps) for a total of 4 apps running at once on MIUI 12.
Now when you have a floating app, the split screen button in the recent menu is gray out, limiting you to just 3 apps running at once, unless you know the workaround or use third party app.
Also, the "custom" floating window doesn't always open, for example, if you have a floating app running already, most "custom" floating window can't open until you close the floating app.
Another example, maps, when having a route, pressing the home button used to cause the floating window to pop up but now doesn't, instead it only pop up when opening the recent app and from there you can exit to home to have it remain open.
MIUI also limits floating window to 1 even via scrcpy second screen desktop mode which even my older 5x slower phone happily allow while lagging like crazy,
I ain't too sure about the state of custom firmware but if it's stock android, it might allow multiple windows and probably doesn't have all those issue
I have a POCO F3 and I used to be able to split screen while having a floating app and an app specific "custom" floating window (eg: vlc, youtube, newpipe, maps) for a total of 4 apps running at once on MIUI 12.
Now when you have a floating app, the split screen button in the recent menu is gray out, limiting you to just 3 apps running at once, unless you know the workaround or use third party app.
Also, the "custom" floating window doesn't always open, for example, if you have a floating app running already, most "custom" floating window can't open until you close the floating app.
Another example, maps, when having a route, pressing the home button used to cause the floating window to pop up but now doesn't, instead it only pop up when opening the recent app and from there you can exit to home to have it remain open.
All those dumb "rules" on which order and how I need to open my apps/games and close them to avoid it bugging out,
worse common case is when a video in it's custom floating window ends then I need to close both split screen app, close the floating app and then I can finally open the video app to change the video.
If I jump straight into the video app, The floating window can't reopen due to the floating app, if I close the floating app, I can't reopen it due to the split screen, so I end up needing to close everything to change a video, if I didn't do it in a specific order, it sometimes bug out and throws "some app are opened in floating windows".
Which has it's own set of "rules" to fix it, or in most cases, I just reboot the phone because it's stupid and other bugs might appear
worse common case is when a video in it's custom floating window ends then I need to close both split screen app, close the floating app and then I can finally open the video app to change the video.
If I jump straight into the video app, The floating window can't reopen due to the floating app, if I close the floating app, I can't reopen it due to the split screen, so I end up needing to close everything to change a video, if I didn't do it in a specific order, it sometimes bug out and throws "some app are opened in floating windows".
Which has it's own set of "rules" to fix it, or in most cases, I just reboot the phone because it's stupid and other bugs might appear
MIUI also limits floating window to 1 even via scrcpy second screen desktop mode which even my older 5x slower phone happily allow while lagging like crazy,
I ain't too sure about the state of custom firmware but if it's stock android, it might allow multiple windows and probably doesn't have all those issue