V$SESSMETRIC data unavailable inside PDB

Select from V$SESSMETRIC for PDB in multitenant database returns no rows:

 connect SYS…

 alter session set container = cdb$root;

 select count (1)

   from SYS.V$SESSMETRIC;

 -- OK

 alter session set container = pdb1;

 select count (1)

   from SYS.V$SESSMETRIC;

 0

Is it a bug? I have found no documentation about unavailability of this view in PDB.

Tested on XE 18 on Windows, 19.8 win64, 19.9 Linux.