Tomcat 11启动时触发UnsupportedClassVersionError错误的原因排查求助

大家好，我安装了Tomcat 11.0.0-M6，但每次尝试首次启动它的时候都会弹出下面这个错误：

Error: LinkageError occurred while loading main class org.apache.catalina.startup.Bootstrap

java.lang.UnsupportedClassVersionError: org/apache/catalina/startup/Bootstrap has been compiled by a more recent version of the Java Runtime (class file version 61.0), this version of the Java Runtime only recognizes class file versions up to 55.0

我已经通过执行java -version命令检查了Java版本，结果显示是Java 11，对应的类文件版本是55.0，本来应该符合Tomcat的要求才对：

java version "11.0.12" 2021-07-20 LTS
Java(TM) SE Runtime Environment 18.9 (build 11.0.12+8-LTS-237)
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.12+8-LTS-237, mixed mode)

之后我又执行了update-alternatives --display java命令，输出显示当前使用的确实是Java 11，而不是Java 17：

java - manual mode

link best version is /opt/jdk/jdk-11.0.12/bin/java

link currently points to /opt/jdk/jdk-11.0.12/bin/java

link java is /usr/bin/java

/opt/jdk/jdk-11.0.12/bin/java - priority 100

/opt/jdk/jdk-17.0.7/bin/java - priority 100

/opt/jdk/jdk1.8.0_301/bin/java - priority 100

下面是我的tomcat.service文件内容：

[Unit]
Description="Tomcat Service"
After=network.target

[Service]
Type=forking
User=tomcat
Group=tomcat
RestartSec=10
Restart=always
Environment="JAVA_HOME=/opt/jdk/jdk-11.0.12"
Environment="JAVA_OPTS=-Djava.awt.headless=true -Djava.security.egd=file:/dev/./urandom"
Environment="CATALINA_BASE=/opt/tomcat"
Environment="CATALINA_HOME=/opt/tomcat"
Environment="CATALINA_PID=/opt/tomcat/temp/tomcat.pid"
Environment="CATALINA_OPTS=-Xms512M -Xmx1024M -server -XX:+UseParallelGC"
ExecStart=/opt/tomcat/bin/startup.sh
ExecStop=/opt/tomcat/bin/shutdown.sh

[Install]
WantedBy=multi-user.target

[Service]
Environment="CATALINA_OPTS=-Djava.library.path=/usr/java/packages/lib/amd64:/usr/lib/x86_64-linux-gnu:/usr/lib64:/lib64:/lib:/usr/lib"

有没有大佬能帮我分析一下，到底是什么原因导致这个错误的呀？非常感谢大家的帮助！

备注：内容来源于stack exchange，提问作者JBD