@granddaddyopera The answer for the title is no.
Opera GX came from standard Opera, so it should have everything that the standard version has. With that said, they will remove things only for a reason
My guess is because of the design. They might bring it back in the future, hopefully, with an option to enable/disable it (I really prefer a single sidebar but having more options is always better).
Also, everything you could do to request this was already made with your post, because there's no dedicated "Opera GX Feature request" forum, so you must have faith that some dev will read this topic.