1 has different meanings. Poetry means "poetry" and is a countable noun, which can refer to a specific poem, two poems, several poems and so on. Although poetry also has the meaning of "poetry", it is the general name of poetry and an uncountable noun; When used as the subject, the predicate verb is always singular.
2. The usage is different. When a poem is the subject, the number of predicate verbs depends on the number of poems (that is, the poem is singular and the predicate verb is singular; Poetry is plural, predicate verb is plural). The usage of poetry is mostly used for the subject.
3. Countability is different. Poetry is a countable noun, which can have plural form and can be followed by-S. Poetry is an uncountable noun, which is a general term for poetry. There is no plural form and it cannot be followed by-S.