admin users with all permissions does not have option of "Show All Domains' under Metrics/Traces By Agent menu option.
"Show All Domains' check box is missing for admin users even with all permissions selected. It is also missing for user with the role of tenant admin. It is only available for out of the box tenant admin that is being created at the time of DX SAAS tenant setup.
DX SAAS
We have following information on the current design and behavior for "Show all domains".
Based on the APM side code, this seems to be an existing behavior. The "Show All Domains" is only shown for a "Tenant Admin". For a custom role (even if the permissions are same as the TA), this checkbox should not be shown.
with Release 25.1 the new RBAC has changed the behavior of "Show all domains".
There has been significant changes in the behavior for this control and in certain cases it will be available unconditionally.