As long as it is the official Proton version from Valve. Bug reports can be filed here:
https://github.com/ValveSoftware/Proton/issues

Originally posted by KingyWingy:

What is the significance of the check box to confirm that I have not found a compatibility report for the applicable game?

To remind you to search rather than filling up the bug tracker with duplicates. Duplicates will be closed regardless.

That is not what I am asking.

If I have 3 bugs to report for a game. Do I make a new compatibility report Issue for each bug. Or do I post in the existing compatibility report Issue someone else made. Or are neither of these correct?

Originally posted by KingyWingy:

That is not what I am asking.

Yes, it is.

If I have 3 bugs to report for a game. Do I make a new compatibility report Issue for each bug. Or do I post in the existing compatibility report Issue someone else made. Or are neither of these correct?

Each game has only one live issue on the tracker (all others being closed as duplicates). If you've found Proton issues with a particular game, report them on that issue. Feel free to put each distinct issue in a distinct comment if you're feeling tidy.

If you can properly proof they are separate from one another, then yes, each should have their own report.

But some games do have multiple Github Issues, for example Doom 2016.
https://github.com/ValveSoftware/Proton/issues/7871
https://github.com/ValveSoftware/Proton/issues/3548

Edit: Looks like we are all confused.