There's no mention of Output Management Web Viewer in the processor compatibility matrix.
Can you pls confirm if v14 and v12.1.6 build 218 are ok on z16s?
Release : 14.0
Component : Output Management Web Viewer
there is no 12.1 Web Viewer processor compatibility statement because, it runs as more of distributed application than a mainframe one.
For 14.0 Web Viewer however, Broadcom creates a single matrix across all products for z16 compatibility - IBM zEnterprise Compatibility Matrix
https://ftpdocs.broadcom.com/
Web Viewer r14 is a component of View which is listed in the matrix: