You can only select the BOM there that is tied to the assembly. When i go to build assembly - I should have components populate to build that item and it is not working

The BOM drives the list of components added to the work order or assembly build. Check if you have a BOM set as Master default and a Revision with the list of components added to that BOM

Yes - I did some auditing and someone in the company had accidentally checked and turned on Advanced Bill of Materials - causing this issue.