Answer
Before migrating, pull your ERP vendor's supported platform matrix for the exact Power generation and IBM i release you are moving to, and do the same for smaller third-party pieces of the stack such as EDI connectors, barcode and warehouse integrations, and document management tools. Most of it moves cleanly. The exceptions tend to be older middleware, custom Java integrations pinned to a specific JVM version, or point-to-point interfaces built years ago that nobody has revisited since, so those are the pieces worth revalidating first.