Do we have any online site where we can create SharePoint Demo portal with master page and page layouts? I need to try a few things for a testing purpose.
I have a test SharePoint site set up, you will be able to create this via https://docs.microsoft.com/en-us/office/developer-program/office-365-developer-program-get-started
You have a 12 month subscription with this program.
Hope this helps.
You could apply a free developer SharePoint Online subscription for One Year, please visit here for register:
I think this will meet your test purpose.
You can subscribe 30 days trail version of SharePoint online by using This link
It depends ;-)
https://demos.microsoft.com/ is available for Partners and each MSDN subscription comes with a free tenant for dev and test