Adminpanel: Disable pagemedia upload or disable multiple upload

Hey everyone,
Is there a way I can disable the default pagemedia form field or that I can make sure that the user can only upload one file in the pagemedia form field?

I tried adding this to my ../themes/mytheme/blueprints/event.yaml:

uploads:
  multiple: false

But this doesn't override the default behavior of the pagemedia form field.

You have to override the system/blueprints/pages/default.yaml by copying it and modifying it your theme, ie: user/your_theme/blueprints/pages/default.yaml. Full details on what you can do to remove fields etc can be found in the docs under Advanced Features.