Based on the knowledge sources available, I can see how board-wide filters work, but there isn't explicit documentation about a way to make an individual report fully ignore a parent (board-level) filter.
Here's what the documentation does say about board-wide filters:
"Applying date ranges and filters on a Board does not alter the queries saved in individual reports. Instead, it updates the data displayed when you view those reports on the current Board." [Board Filters]
This means board-level filters are applied on top of the individual report's saved query when viewed from the board. The knowledge sources do not describe a built-in mechanism to exempt a specific report from a board-wide (pinned) filter.
What you could consider as a workaround:
Save the report to a different board that doesn't have the parent filter applied. Since reports are not contained to a single board, the same report can exist on multiple boards with different filter contexts. [Saved Content in Data Views]
Access the report directly (not via the board). When you navigate directly to a report (not through the board), it will display the report's original saved filters without the board-level filter applied. [Board Filters]
For a definitive answer on whether there's a way to exclude a specific report from a board filter, I'd recommend reaching out to Mixpanel Support, as the knowledge sources don't explicitly cover this use case.
