Ruby 4.0.1 has been released with a few fixes we should confirm on JRuby:

• Bug #21812: Kernel#sleep without arguments returns immediately when subprocess exits in another thread (regression in Ruby 4.0) - Ruby - Ruby Issue Tracking System
• Bug #21828: An incorrect warning message related to benchmark is shown when using benchmark-ips - Ruby - Ruby Issue Tracking System
• Bug #21811: Fix underflow in Array#pack - Ruby - Ruby Issue Tracking System
• Bug #21814: 0.pow(2,-9999999999999999990) should be zero - Ruby - Ruby Issue Tracking System
• Bug #21819: A Data object should be frozen even if it has no members - Ruby - Ruby Issue Tracking System