If you want to provide confidential / private information, typically for a public bug report, do the following:

1. Report a new problem here: https://developercommunity.microsoft.com/dotnet/report. Briefly explain that you just want to provide private information to a public bug (add a link to the public bug).
2. Once the report has been opened, you can add private attachments to it.
3. Also post a link to the report in the public bug, so that we can easily cross-reference them.

We'll close the report once we've cross-referenced them, but it's still possible to attach more private attachments if needed, even if the report is closed.