Create custom button in Mobile Freedom UI and run a business process

For a nocode approach, probably you need to wait for the "Mobile App Wizard overhaul " & the "Freedom UI Designer for mobile"  planned for later in the year if all goes according to plan

You can add custom button in Mobile Freedom UI using Mobile Application Wizard. You can find out more details in this article
https://academy.creatio.com/docs/8.x/dev/development-on-creatio-platform/8.1/mobile-development/customization/freedom-ui/customize-page/customize-page-mobile

Also you can find the instructions how to run a business process by clicking the button in the following article in the section "Set up a button that runs business processes in a section"
https://academy.creatio.com/docs/8.x/no-code-customization/customization-tools/ui-and-business-logic-customization/element-setup-examples/components/set-up-button-components