I have an MSCS that I took a decade after undergrad and while switching from MechE to CS. An MS won’t really teach you fundamentals, and it won’t make you stronger at the fundamentals you already know except by giving you a structured environment within which to practice and refine those while doing the work. I think the MS mostly helped me to learn more depth over a curated breadth of concepts than the BS that emphasized fundamentals.

The credential may be valuable to open doors that are artificially closed to you as someone without a degree. Even with a BS in MechE and programming experience I had a hard time getting interviews, but as soon as the MSCS hit my resume I started getting unsolicited calls. YMMV.