The following prompt is controlled by the PCS / PPS administrator. Also, we are making further improvement in our next major release in 8.3/5.4 so the administrator can enforce an min. version of Pulse Desktop for any user connecting to their device.
If you are the admin, the following option can be disabled under System > Options > uncheck "Enable web installation and automatic upgrade of Pulse Secure clients". The behavior change would be client will no longer see the prompt, but also the end user would no longer be able to downloaded the Pulse client from the web interface. This is only recommended if the admin is decided to deploy the Pulse client outside of the PCS/PPS environment like group policy or other means.
If you an end user, there is no way to disable the following prompt. Please talk to your PCS/PPS administrator.