adobe stager material i download from creative cloud not showing in material panel?

Right. That not a bug There is update of materials list for 3.0. So some of materials are removed by team. https://helpx.adobe.com/substance-3d-stager/release-notes/version-3-0.html#:~:text=Expanded%20starter%20material%20library

I think you misunderstood me. In this screenshot from the older Substance 3D Stager 2.1.4 version, they are available in Materials in the Stager Assets Panel, but they disappear in the new version 3.0.2. It's definitely a bug.

I mean Materials in Stager Assets Panel not in Project Material Panel. For Project Material Panel you are right-it save there for custom file.

I just wanted to let you know that I think you might be mistaken about Adobe Stager. I've actually used the materials downloaded from the Creative Cloud Desktop app and sent them straight to the app, and they always show up in the material panel for me.To double check, I even tested it out—I removed the newer 3.0.2 version and installed the older 2.1.4 version instead. And yep, it worked perfectly! The materials still went right into the material panel. So I'm pretty confident that your statement about Stager not being able to install materials directly on the panel isn't accurate. It's definitely a bug.

You can keep it in CC Library. Adding user material in material panel (as for Substance Painter, Sampler) is not available in Stager