Whenever I test Steam support, it works fine for me - both on PC running with Steam or on the Steam Deck. That indicates everything on Construct's side is working OK - if it wasn't, then it wouldn't work when run in a test or development environment. If there's a problem with publishing, then that is all happening on Valve's side, and it's beyond our control - for example if there is some bug or issue with Valve's upload or publishing process, we can't fix it for them, nor is it reasonable to expect us to do so. So I'm afraid it is one of the times you have to go to another company for support with that, as it's not something we are involved with.
We don't have titles that we publish ourselves, so it's a difficult thing for us to test. However it's one of these things where even if we did try to publish something ourselves, and it is broken because of something on Valve's side, it doesn't change much - we would still need Valve to fix it. So I don't think that makes too much of a difference here.
AFAIK there are Construct users who are publishing titles to Steam, and the process isn't significantly different between NW.js and our newer export options, so I would assume this is working for at least some people. I'd guess that there is some configuration issue, mistake, or bug that only some people are running in to; if we can figure out what that is then hopefully it would be all sorted. But I would encourage you to go to Valve first, as I don't think there is much we can do about this.