If I open standy database with upgrade option and complete the upgrade that causes a problem on primary side ?
could be any problem at role transition or after role transition
If you upgrade standby database successfully, then you can switchover to standby database.
Then you can upgrade new standby to 126.96.36.199 version, too.
Please check this article : www.oracle.com/au/products/database/maa-wp-11g-upgrades-made-easy-131972.pdf
Mahir M. Quluzade
Could I open standby with open upgrade command as you know standby is only opening read only ?
also Could I switch primary to standby and standby to primary again without upgrade primary ?
Thanks alot for your attention