We had a similar issue with Identity Server and OIDC, though I'm not sure the setup was exactly the same. For us, the generated login/auth pages were located under:
(Project) > Areas > Identity > Pages > Account
Here is a screenshot, you can also try to search the project for some of the file names.
![folder structure]()
However, despite using the React template, and doing everything in React, the auth components were MVC (or Razor or something, can't remember). So we ended up building our own client pages, setting up routing and building custom controller actions to talk to Identity server. We got it to work in the end, but it was way more trouble than it should have been, to be honest.