Remove element by Key
Also
KeySelect[StringStartsQ[Except @ "_"]][asso]
<|"key1" -> {}, "key2" -> "string"|>
asso // KeyDrop@Select[Keys[asso], StringStartsQ["_"]]
Also
KeySelect[StringStartsQ[Except @ "_"]][asso]
<|"key1" -> {}, "key2" -> "string"|>
asso // KeyDrop@Select[Keys[asso], StringStartsQ["_"]]