Hi Aizaz,

Thanks for your reply again.
I just found out what the problem was and I sincerely hope this will help others.

Sidebars won’t show if Elementor Full Width or Canvas template are used as page attribute.
Creating own template with sidebar functionality or just the default theme template will enable the sidebar.

Now, I know the following is off this topic but maybe you can through a rapid solution for this.

The theme custom metabox for page settings moved to the editor’s side (see screenshot).

Thank you so much!