"deprecate"? or "depreciate"? Does it mean they will no longer promote it, or no longer support it?"

"Deprecate" and yes to both.

It's a systems integration word for dropping a module or subsystem from the process specification. For software it's the Application Programming Interface (API.)

The product manager and team go away. Developers are on notice to transition to the newer process module. Quality engineers can ignore it during validation.

Plan on the first few (non)mandatory W10 updates going poorly if you decide to keep it.