Glossary
Adaptive Card Extension (ACE)
An Adaptive Card Extension is the component type behind the cards on a Viva Connections dashboard. It is built with the SharePoint Framework, like a web part, but renders as a small fixed-size card rather than as page content.
Because it is a different component type, an existing web part does not simply appear on the Viva dashboard. The intended pattern is a card that links to the page holding the web part.
Building a custom one is SPFx development, with the same toolchain, packaging and ongoing maintenance as any other component. Budget for it the same way.