A field group in PHP or as a JSON file will not show up in the ACF admin unless you import a JSON file.
If a JSON file exists in the themes acf-json folder, that field group will be loaded without showing the field group in the ACF admin it the field group does not already exist there. You can set multiple load points. So you could have your plugin have it’s own folder for loading JSON files from. However you can only have one save point, so when editing field groups in ACF the JSON files can be automatically saved, but only to one location.
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