Surely you have tried to uninstall an application from your mobile and you have realized that this option is not available or is disabled. It is common in system applications or pre-installed as standard, but this does not imply that you can not disable it.

With your Huawei P9 Lite that works on the EMUI customization layer you can disable those applications which means that they will not be available from the app drawer nor will it start at the start of the mobile and any update will be uninstalled beyond the pre-installed version. Let’s see how to do it.
Pre

With EMUI the step to disable preinstalled apps is simple. We just have to go to the list of applications from Settings and once inside select the application that we want to disable. To illustrate this step we have chosen the Gmail app:
https://imgur.com/v55q0kI

As you can see we do not have the option to uninstall but we can disable it, by pressing that button in question. This step implies that this application will not appear more than in this list of apps from Settings and that, in case you want to use it later, we will have to re-enable it and update to the latest version from the Play Store.