Check below Microsoft official documentation to figure out if you are using classic experience or modern experience in SharePoint online:
SharePoint classic and modern experiences
Content Editor and Script Editor are classic experience web parts in SharePoint. If you are using SharePoint online modern experience, those will not be visible on SharePoint pages while adding web parts.
For SharePoint online modern experience, you have to use the custom script editor web part developed using SPFx by community memebers.
You can find it at: Script editor web part for modern pages built in React
Check below Microsoft official documentation related to deploying SPFx web parts in SharePoint online: Deploy your client-side web part to a SharePoint page