I tried the Twenty Twenty theme but it did not bring back the left margin and brought in new problems
I use these privileges which have not created problems with two earlier installations of wpForo but there have been updates since then, so I thought to check:
remove all Custom CSS codes, and try the below Themes:
https://wordpress.org/themes/shuttle-ibusiness/
https://wordpress.org/themes/astra/
I was/am using Astra because it was good with earlier wpForo however you do prove that the theme is the problem as Shuttle allows the left margin and reduces the middle column width which I want.
But it introduces new issues that I don't want:(
About Shuttle theme,
You can set the Main Menu in that place and left the top left Menu empty.
Press the Customize Button from Dashboard Top bar, Navigate to Menus > View all Locations and set the Menus Like the Below Example:
wpForo Menu: wpForo Navigation
Pre Header Menu: Empty
Primary Header Menu: Your Main Menu
I tried those modifications but couldn't make it work. However I did notice that reCapture was working with Shuttle but I think the Astra guy was working on the site at the same time so I was not able to continue.
But it does show that the main issues are coming from that Astra Theme. I will keep you posted if I can make some progress.
Thank you.