See SAP OSS 727139/2020 for details.
I’m proud to inform that SAP has finally released a fix for this problem : 2990918 – DBA Cockpit: SAP Screen Personas in DBA Cockpit not supported.
How to fix constant spinning cursor: execute report RSDBAFORCEACCEXPLAIN to reset Java-based and HTML5-based query plan display back to generic ALV tree-based for the current SAP logon user.
See SAP Notes 2212966 – SYB: Report to disable Java plug-in in DBA Cockpit EXPLAIN, 2199314 – IBM i: Enablement of HTML5 (JavaScript) container for EXPLAIN screens