Update README.md

Author: Waitsnake

README.md

@@ -15,16 +15,20 @@ This project was originally (release 1.0) written with Xcode 6.2 and SDK for OSX
 
 The release 1.4.0 was compiled with Xcode 10.1 with SDK for OSX 10.14 Mojave. It was tested successfully under Mavericks(10.9.5), El Capitan(10.11.6), High Sierra(10.13.6) and Mojave(10.14.5).
 
-The latest release 1.5.3 was compiled with Xcode 10.2.1 with SDK for OSX 10.14 Mojave. It was tested successfully under Mavericks(10.9.5), High Sierra(10.13.6) and Mojave(10.14.6).
+The release 1.5.3 was compiled with Xcode 10.2.1 with SDK for OSX 10.14 Mojave. It was tested successfully under Mavericks(10.9.5), High Sierra(10.13.6) and Mojave(10.14.6).
 
-_Note: AnimatedGif is **not working** with **Catalina(10.15**) and **Big Sur(11.0)** since screensavers are now sandboxed (this means no GIF files can be selected or read from local disk and also background mode is broken), see issue <a href="https://github.com/Waitsnake/AnimatedGif/issues/57">#57</a> and <a href="https://github.com/Waitsnake/AnimatedGif/issues/63">#63</a>._
+The latest release 1.5.4 was compiled with Xcode 12.5.1 with SDK for macOS 11 Big Sur. It was tested successfully under High Sierra(10.13.6), Mojave(10.14.6) and Big Sur(11.5.2).
+
+_Note: AnimatedGif is **not working** with **Catalina(10.15)** and early versions of **Big Sur(11)** (later OS versions of Big Sur make Sandbox more open and allow selection of local user files) since screensavers are sandboxed (this means no GIF files can be selected or read from local disk and also background mode is broken), see issue <a href="https://github.com/Waitsnake/AnimatedGif/issues/57">#57</a> and <a href="https://github.com/Waitsnake/AnimatedGif/issues/63">#63</a>._
 
 Since release 1.5.0 AnimatedGif supports Metal(API) for rendering.
 
 When started AnimatedGif tries to initialise Metal as first choice for rendering. Only if this initialisation fails (on MacOSX versions older than El Capitan (10.11) or not supported Macs(usually Macs older as Mid 2012; except Mac Pro models from Mid 2010 with supported graphics card)) it tries to initialise OpenGL for rendering(as it was default between release 1.0 till 1.4.0).
 
 Unfortunately the screensaver clock is not working together with background mode and will be disabled if background mode is enabled. But the clock works fine in normal screensaver mode.
 
+Because Big Sur(11.5.2) still sandboxes screensaver the background mode is still not working and so this button will be automaticly disabled since release 1.5.4 when Big Sur(and Catalina) is detected. But background mode is still available on Mojave or earlier versions of OSX.
+
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 ## Setup - Mac