I also use Jellyfin. Before being able to set custom tag delimiters, you had to ensure your music artists and album artists ID3 tags were correct. I believe it used a ‘;’ to separate multiple artists. Now with custom delimiters you can set your own. You may be able to try and fix things by setting ‘feat.’ as a custom tag.
Ultimately, I would recommend just using mp3tag and spending a few minutes setting up an action that replaces ‘feat.’ with a delimiter, such as a ‘|’. Run it through your current library and you should be good.
I also use Jellyfin. Before being able to set custom tag delimiters, you had to ensure your music artists and album artists ID3 tags were correct. I believe it used a ‘;’ to separate multiple artists. Now with custom delimiters you can set your own. You may be able to try and fix things by setting ‘feat.’ as a custom tag.
Ultimately, I would recommend just using mp3tag and spending a few minutes setting up an action that replaces ‘feat.’ with a delimiter, such as a ‘|’. Run it through your current library and you should be good.