There is no menu bar in the Online version and you’ll find the menu items in the contextual menus of the catalog, furniture list, plan and 3D view. I know that for some Mac users, it’s not so common to use contextual menus, and I hope you’ll get used to them quickly: just click on a part of the program while pressing the ctrl key or configure right clicks in system settings.

My computer is now so old that I just don't have the memory to support it anymore.

What makes you think it can’t work?