It turned out to be very simple:

all I needed to do was to first group the controls and charts by selecting them all and doing Arrange > Group then add (again) the score card that I needed not be affected by the controls which would not be included in the previous grouping

after that selecting anything on the controls on the dashboard will not affect my out-of-group score card last added.

source: https://cloud.google.com/looker/docs/studio/apply-controls-to-specific-charts