Per System requirements, it strictly say Postgres 9.6.x, so no, Postgres 11 won't support it and if you continue, do this at your own risk ( that means, if you manage to install it, but later on you have issue and come to conclusion it is the Version of postgress, Qlik won't implement a fix for it).
Read more:
https://help.qlik.com/en-US/sense/June2019/Subsystems/PlanningQlikSenseDeployments/Content/Sense_Dep...
Giuseppe Novello
Principal Technical Support Engineer @ Qlik