To make a quick action available on the Salesforce mobile app, you need to add it to the Salesforce Mobile and Lightning Experience Actions section of the page layout. You can use the Page Layout Editor to drag and drop the quick action onto the section.
References: https://help.salesforce.com/s/articleView?id=sf.actions_in_lex.htm&type=5 https://help.
salesforce.com/s/articleView?id=sf.customize_page_layouts.htm&type=5