Hi,i really enjoy the sigma theme.

Naturally that there allways some files that need to be changed in order to adapt for some plugins, but usually one want's to change, adapt, something in the look.

So i selected sigma the be start engine of my Osclass, with some adjustments and changes in the look, it'll be an awesome starting Point, most likely for the next theme I'll go with Veronica, but for my testing and learning i'm starting with sigma.

For that, i would like to duplicate sigma to a new theme and do my changes there.

I followed instructions on this page: https://docs.osclasspoint.com/how-to-create-theme.

However the new theme doesn't show on the Appearence/Manage Theme option in Osclass admin interface.

The summary steps for doing copying the theme were as follows:

1 - copied the folder form osclass/oc-content/themes/sigma to osclass/oc-content/themes/new-theme-sigma.

2 - opened the files with IDE, made a find and replace in all files: find "sigma", replace with "new-theme-sigma".

The new theme however does not show in the "Appearence/Manage Themes" Option".

Any missing step ? or an idea where to check ?

Self solved 

Just renamed the theme to my theme_sigma and did a find and replace in all theme files to this new name and it was solved.

The problem might have been using "-" instead of "_" or perhaps the theme name size.

I'll start working on my new sigma and learn how Osclass works before going to a new theme 

There are still some issues to solve in sigma, and learning to do before going to a full fledge and well built theme like the ones in osclasspoint maketplace.
i.e.: image problems with rotation and exif data, and some weird ads spacing in the main page, as if there were some ads missing.

You can check-out these at www.atol.pt, if you have any ideia what it might be let me know.

Also, still trying to figure out what is the best approach, to duplicate a theme or to use a child theme.

Sorry to bother.

I recommend to use theme name without - or _ symbols, i.e.:
sigma2