Cannot compile with maven following INSTALL.md instructions

[benjub]

On Debian, I followed the instructions from the paragraph "Building mmj2 with maven" of INSTALL.md up to

$ mvn package
[INFO] Scanning for projects...
[INFO] 
[INFO] ------------------------------< mmj:mmj2 >------------------------------
[INFO] Building mmj2 2.5.2-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ mmj2 ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /home/benoit/Documents/personnel/metamath/git/mmj2/src/main/resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ mmj2 ---
[INFO] Changes detected - recompiling the module!
[WARNING] File encoding has not been set, using platform encoding UTF-8, i.e. build is platform dependent!
[INFO] Compiling 357 source files to /home/benoit/Documents/personnel/metamath/git/mmj2/target/classes
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  0.321 s
[INFO] Finished at: 2023-07-28T22:37:33+02:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project mmj2: Fatal error compiling: invalid target release: 11 -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException

I do not know maven at all so I do not understand these messages. I can post the outputs with the -e and -X options if needed.