You can choose whether to have sidebar on individual post and pages, or in general in the customizer.. Companion not needed.
https://creativethemes.com/blocksy/docs/post-types/blog-posts/
Bjarne
Thank you so much for your help.
I do have another question. I discovered today when I visit the website via ny smartphone that in the menu there is a download button! What does it do and how cab I remove it?
@block24 That button is just for demonstration purpose, you can remove it any time, simply go to Customizer -> Header -> Mobile Header and remove it from the off canvas panel – see the screenshot.
Let me know if you have any other questions.
Great, thanks for your help again! great support