A very brief search turned up assorted overviews[1][2][3], and a github topic[4]. The PLCopen standard[5] is paywalled - only $400 single user, with low low per-seat multipliers! :/
[1] https://en.wikipedia.org/wiki/IEC_61131-3 [2] https://dc-us.resource.bosch.com/media/us/products_13/produc... [3] https://www.controleng.com/articles/which-iec-61131-3-progra... [4] https://github.com/topics/iec61131-3 [5] https://plcopen.org/iec-61131-3