Describe the feature you'd like to have added

In the place of where other variants of the item card would have a button for "exact mode", for the sensor variant, have a button for "detect mode".
Let the button switch between "Inventory contents" and "Block type", where the former is the current behaviour of the sensor, and the latter is the new behaviour. The new behaviour allows the sensor to check the type of the target block itself, rather than any items inside of it.

This behaviour is still relevant for the item card, as opposed to requiring a useless "block" card, since you still would specify its filter in terms of items. For instance a normal filter with a cobblestone item in it, would allow the sensor in block mode to test whether the target block is a cobblestone one.

This does mean the sensor can only detect blocks that have an item form. However, it should be possible to find matching blocks anyway if an item doesn't have an immediately matching block, if it produces one upon use (e.g. wheat crops from seeds).

This feature would be useful to have, so you can for instance base your redstone signals on the presence or distinction of a block, such as for a tree farm or for a situation-sensitive block placer.

Additional information

Having written this, I realize there should be a "Fluid source type" option as well.