Setting it to true doesn't make deepers drop all blocks, but reduced amount like normal creepers.
Setting it to false makes them not break blocks at all.

This is due to setting https://github.com/team-abnormals/caverns-and-chasms/blob/1.20.x/src/main/java/com/teamabnormals/caverns_and_chasms/common/entity/monster/deeper/Deeper.java#L152 To MOB instead of TNT and NONE instead of MOB.