Apart from naming conventions there aren't any specific conflicts between the Moodle Code styling (MCS) and PSR for class declarations.

However, both MCS and PSR have requirements in addition to each other.

Required decision:

How are we going to handle the differences between MCS and PSR? Should MCS continue to have extra requirements or should it be only what is defined in PSR?

MCS: https://moodledev.io/general/development/policies/codingstyle#classes-1 

PSR: https://www.php-fig.org/psr/psr-12/#4-classes-properties-and-methods