How do I make a good database diagram if my database is missing a lot of foreign key relationships?

I would prefer not to have to do it by hand and am hoping that there is a good tool that can get me most of the way there and then allow me to keep adding relationships to it manually since we are missing a ton of foreign key relationships. What is a good way to do this? So far I've tried: 1. SSMS database diagram, but it isn't useful because we don't have all the FKs set up and because I can't manually add lines to show relationships without actually going ahead and creating the FKs 2. Doing it by hand in Excel - very time consuming 3. Visual Studio LINQ to SQL - I installed it, but it doesn't show up when I try to add new item and search for it 4. Visual Studio EF Core Power Tools - when I try to create a diagram, I get this error: