Hi,
1) Could you be able to create App from SharePoint list using PowerApps Studio, or PowerApps studio in Web?
- Yes, I'm able to create PowerApp from PowerApps studio Web.
2) In addition, did you make any customization with this list?
- No, it is normal list with some custom fields.
3) Please take a try to create a new custom list, see if that would have the same symptom.
- I have created new custom list but still "Create Power App" option is not available. Please find below screenshot.

One question regarding PowerApp intergration into SharePoint list:
Is there any way to integrate PowerApp to SharePoint list which created using PowerApps studio Web?
Thanks