Android 11 reports an error during OTA package:

ExternalError: Failed to run signapk.jar: return code 1:
Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main" java.lang.UnsupportedClassVersionError: com/android/signapk/SignApk has been compiled by a more recent version of the Java Runtime (class file version 53.0), this version of the Java Runtime only recognizes class file versions up to 52.0
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(ClassLoader.java:756)
	at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
	at java.net.URLClassLoader.defineClass(URLClassLoader.java:468)
	at java.net.URLClassLoader.access$100(URLClassLoader.java:74)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:369)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:363)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:362)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:352)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
	at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:601)

According to the error analysis, it is caused by the jdk version.

1. First check the jdk version: java –version My previous version was openjdk-8
2. Use sudo apt-get install openjdk-11-jdk to install openjdk-11
3. Configure linux default jdk version: sudo update-alternatives –config java, select the JDK version you need
4. Configure the default java version: sudo update-alternatives –config javac, select the java version you need.

Just do the ota package again.