Fedora 31 Beta freeze exception bug tracker: http://fedoraproject.org/wiki/BugZappers/HouseKeeping/Trackers
To propose a bug as a freeze exception bug for the Fedora 31 Beta release, mark it as blocking this bug, or use the webapp: https://qa.fedoraproject.org/blockerbugs/propose_bug . It will be reviewed according to https://fedoraproject.org/wiki/QA:SOP_freeze_exception_bug_process .
If you think the bug is sufficiently serious to block the Beta release, instead mark it as blocking the bug F31BetaBlocker. See https://fedoraproject.org/wiki/QA:SOP_blocker_bug_process for the blocker process.