On 29/01/2025 17:52, songbird wrote:
update-binfmts: warning: current package is openjdk-21, but binary format already installed by openjdk-9
Likely it is related to running of .jar files without explicit java command. In a similar way wine may install a handler for .exe files in addition to default configuration for native ELF binaries and #!/... shebangs.
With two JRE packages installed there is uncertainty which one is configured as a handler for kernel. The reliable way is wrappers for every application that specify what particular java version it needs.
There might be low-priority configuration options for jre packages or some tools to manage priorities in binfmt-related package. Almost certainly you can disable the feature completely.