Migrations are core are now plugins, not config entities. This module used to provide only the config entity list builders and forms on-top of that config entity, which now, no longer exists.
The config entity will be added to migrate_api in #2677196: Re-introduce migration config entity → and then the UI can be re-worked to use a migration plugin as a template/starting point, and a way to create entire new migrations from the UI that will be shimmed into the plugin definitions.
Development
Yes, I imagine the migration you're starting from will be selected from the UI, or you can select non at all.
Yes, likely.
Yes, likely.
Needs work
1.0
Code
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
This module has been marked unsupported and obsolete.
Linking this up with ✨ Show migrate plugins on the Migrate UI lists Active and ✨ UI will not display migrations that are not in configuration. Active as I have not found any UI solution that displays migration Plugins.