Currently there is no SharePoint online out of the box web part available for your requirements to show the site owners on page.
You will have to develop a custom web part using SPFx on your own for your requirements.
Check below documentation to get started with SPFx and SPFx web parts:
- Overview of the SharePoint Framework
- Build your first SharePoint client-side web part
Check this GitHub repository where all custom web part samples submitted by community contributor are available: SharePoint FrameWork client-side web part samples - this will help you to get started with
You can easily get the associated owners group of a SharePoint site using PnP JS
// Gets the associated owners group of a web
const ownerGroup = await sp.web.associatedOwnerGroup();
Reference: SP PnP JS - site groups
Once you get the group details and group ID, you can use SharePoint REST API to get the members of group.