According to reply of Head of POCOPHONE Global, 10.3.4.0 stable for POCO which did not release to all regions due to failure test during Stable Beta release in some regions will not release to all regions since they are merging Qualcom's patch and aiming for June release with other improvement.
This means the devs will bundle improvement in 10.3.4.0 + Qualcom's patch + other improvement in June stable release.

If you want to install 10.3.4.0 stable update, you can either change region or install manually. For more information, refer comment of this thread - https://c.mi.com/thread-2127615-1-0.html

If you want to get more information  regarding June Stable, refer this thread - https://c.mi.com/thread-2125381-1-0.html

* Use brower to open the links since Mi Community does not support opening links for now.