Adding some details, by default, RT instructs tools installing perl modules to get the latest version, so if you try to install RT after 2026-04-27, you will get the new version of Plack and RT won’t run. You can install the last compatible version of Plack by specifying the version number: cpanm Plack@1.0051
Updates that are compatible with new and old versions of Plack will be in the next releases of RT.