Why my user custom action only runs on system pages?

Question

I've added some scriptlink via Add-PnPJavaScriptLink PnP function, however, this only get«s called when on system pages (/_layouts/..)

What am I missing here?

The intention is to run some CSS or JS on every SP Site page load. (branding purposes)

SPRegards

Answer 1

The "modern" experiences allow certain user custom actions to be surfaced in the new user interface, but not all user action configurations that are supported by "classic" mode are supported in the "modern" experience. The following table gives a high level overview of the supported custom action locations and how they're surfaced in the "modern" UI:

User custom action location Visible in "modern" UI EditControlBlock
Yes, these entries show up as custom menu items. CommandUI.Ribbon
Yes, these entries show up as toolbar items. All other locations (for example scriptlink)
Sorry, these user custom actions won't work.

https://docs.microsoft.com/en-us/sharepoint/dev/solution-guidance/modern-experience-customizations-customize-lists-and-libraries