Skin cannot be selected.

All skins in every category are unclickable.

The plugin permissions have all been granted, so why are the skins still grayed out and unclickable?

Because you need to add skins from the workshop.

Is there a JSON file with all the skins? I feel the current version is not as good as before. The previous one was automatic.

The configuration has all the necessary parameters to automatically load approved skins.
But according to the new rules, you can't use them, only skins from the workshop. ( And a large number of skins from the workshop will kill your server. )

I will prepare a file with skins (up to 10k) a little later, it will be supported - symbolic cost.

When will it be released?

Until the next game update in November.