Not able to find "use modern for new project" option in settings under design"

Hi @pvramana.blore

The update for 2023.12.0 have removed the classic switch option. So, what ever the project is being created they will be created as modern project only. If you required you can just use the classic activities by applying the classic filter option in activities panel.

If you want to use Screen Scraping or Data Scraping options you can do the below process:
Open your Project.json file and add the below give line below “fileInfoCollection”: ,

 "modernBehavior": false,

Refer the screenshot below for better understanding:

Save the json file and reopen your project, you will be able to to see Screen Scraping and Data Scraping option.
Refer the below image for better understanding:

If you don’t want these options you can remove that particular line i.e. “modernBehavior”: false, from the json file and save the file. Reopen the project again you will project will be in Modern Experience.

Regards