I have created some SPFx webparts and am able to add it into a custom page layout by adding it into the webpartzone as below in the html, and through the use of design manager.
<!--SPM:<%@Register Tagprefix="WebPartPages" Namespace="Microsoft.SharePoint.WebPartPages" Assembly="Microsoft.SharePoint, Version = 188.8.131.52, Culture = neutral, PublicKeyToken = 71e9bce111e9429c"%>--> <!--MS:<WebPartPages:WebPartZone runat = "server" AllowPersonalization = "false" ID = "top_webpart" FrameType = "TitleBarOnly" Orientation = "Vertical" >--> <!--MS:<ZoneTemplate >--> <!--ME:</ZoneTemplate >--> <!--ME:</WebPartPages:WebPartZone >-->
However, instead of allowing authors to change the webpart, I will like to hardcode the webpart in the page layout so that it cannot be changed. I have read how to get a webpart snippet through https://docs.microsoft.com/en-us/sharepoint/dev/general-development/how-to-add-a-web-part-zone-snippet-in-sharepoint#inserting-a-web-part-zone-snippet but the snippet gallery (including Other Web Parts) does not include custom webpart in its list.
How can I get/come up with the snippet for the custom webpart?