Modern script editor web part

Hallo, I need to use the Js modern script editor but it doesn't appear... I've no error with power shell...  I followed these instruction but I have not modified the files in Visual studio Code:

1)https://docs.microsoft.com/en-us/sharepoint/dev/spfx/set-up-your-development-environment

2)https://docs.microsoft.com/en-us/sharepoint/dev/spfx/web-parts/get-started/build-a-hello-world-web-part

3)https://docs.microsoft.com/en-us/sharepoint/dev/spfx/web-parts/get-started/connect-to-SharePoint

4)https://docs.microsoft.com/en-us/sharepoint/dev/spfx/web-parts/get-started/serve-your-web-part-in-a-sharepoint-page

5)https://docs.microsoft.com/en-us/sharepoint/dev/spfx/web-parts/get-started/hosting-webpart-from-office-365-cdn

6)https://medium.com/niftit-sharepoint-blog/add-the-script-editor-webpart-back-to-sharepoint-modern-experience-688a7b7208e4

In manifests.json file I have not modified the cdnBasePath... Maybe is this the reason?

Could you tell me me why?

The modern script  web part doesn't appear:

and

Please help me

Thank you

Alex