Hi,
It is possible to set the filter on Grid or Masonry Grid module in Content Builder. Please enable the “Show Filter” option.
For “portfolio” source: Please select a category, make sure there are sub-categories in this category. The category structure looks like:

For the “Media library” source, you could set category for each image, but don’t set parent category, it will list all categories of level 1 set on images.

More on DOC: https://doc.seatheme.net/static/sea/#filter
Regards!
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