According to the OnePlus 7 Series and OnePlus 7T forum posts (7 Series, 7T), the OxygenOS update comes with 10.3.6 versions for the Indian variants and 10.0.9 versions for the European variants. There is no change in this update as compared to the previous update for the Indian variants of OnePlus 7 series. It includes a new user assistance feature, optimized power consumption, fixes for flashback issues and improvements in system stability.
However, as seen by XDA Developers, some additional fixes are found in the European variants of the phone. In these, the problem of the alarm clock not ringing has been fixed and sometimes the problems with the message.
The update of the Indian variants of OnePlus 7T includes some changes over the previous update. The update comes with version 10.3.6 and brings an alarm clock and message fix for the OnePlus 7T. The previous update (version 10.3.5) of the OnePlus 7T had the same changes as the OnePlus 7.
It is also important to note that OnePlus has not updated the security patches for the OnePlus 7 Series or OnePlus 7T with these latest updates, which still come with the September security patch. It is beyond our understanding why OnePlus has given two similar updates within the same month.