I want to filter N+1 queries (or other performance issue detectors) on the Issues page or I'd like to completely opt out from accepting these.

You can turn of performance issue detectors from your Project Settings -> Performance -> "Performance Issues - Detector Threshold Settings" card, pictured below:
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You can filter your stream to examine all of the Performance Issues a given project is detecting by using the query issue.category:performance .

Note: To deactivate the `Transaction Duration Regression` and `Function Duration Regression` detectors you will need to contact support.