Using C##rmanuser with sysbackup to backup control file to trace fails ORA-1031

Oracle Enterprise Database (19.9)

Looking at switching backups run as sys to using user with sysbackup role.

Existing rman backup script , contains "alter database backup controlfile to trace;"

This fails with ORA-01031: insufficient privileges

Note : sqlplus as C##rmanuser with sysbackup also gives same error,

sysbackup ment to have "alter database" privileges.

Anybody know minimum extra needed by user to be able to "alter database backup controlfile to trace;"

2024/02/29 - update (others asking basic questions).

Rman script "connect target "c##rmanuser/rmanuserpw@targetCDB as sysbackup"

Looking in v$pwfile_users both sysbackup and c##rmanuser in passwordfile.

rman has

run {

# set of backup commands, then