adverb, pronoun, verb, modal particle · used as a resultative verb suffix to indicate the inability to carry out or complete an action

这个行李太重，我提不了。

adverb · used in the pattern {verb} + 个 gè + 不了 to indicate that an action continues without end

他一说起当兵的事就说个不了。

adverb · no thanks (used to politely but informally decline)

你要喝咖啡吗？不了，谢谢。