In answer to a question sent to me by a contributor about rights for poems published on Poets Online - I refer you to the detailed response at
https://poetsonline.org/copyrights.html but here is an excerpt from that page.
Can I Submit My Poem Used Here To Other Publications? That depends on the publication's rules. Many print and online publishers now do not accept work that has been previously published, in print or online. Resubmitting poems for contests and anthologies often waives that rule, and some (Rattle is an example) do not consider self-publishing to blogs, message boards, or social media as publication with respect to this rule. Always read the submission rules carefully for any submission.