Custom buttons and links in the Salesforce mobile app
Key Takeaway
A custom button works in the Salesforce mobile app only when it is in the Button section of a page layout and its content source is URL or Visualforce.
Custom buttons and links are controls an app builder adds to Salesforce pages to open a URL, show a Visualforce page, or run JavaScript. Only some of them carry over to the Salesforce mobile app, so an app builder needs to know which kinds work there and how they appear.
Which custom buttons work in the Salesforce mobile app
A custom button works in the Salesforce mobile app only when both of these conditions are true: it is added to the Button section of a page layout, and its content source is URL or Visualforce.
In Salesforce Classic, a common technique is a URL custom button that passes parameters to a standard page, for example to prepopulate fields when creating a record. This technique does not work in the Salesforce mobile app, so it cannot meet a requirement for mobile users.