Apologies for the late reply.

You can still rate the sellers' performance in various categories out of 5 (as you always could) but it's now optional & hidden & is easy to overlook.

It's titled 'Rate more details about your purchase (Optional)' v

You click the downward arrow to the right of 'Optional' & the categories open up.

On the 'Tell us more about this item' box you just leave your normal feedback.

Above this you sometimes get (depending on the item) 'How would you rate this item? (Optional).

This is the box that caused all the trouble (you originally had to fill this in to leave feedback). However, following numerous complaints, combined with the fact that nobody on the eBay helpdesk knew anything about it, or, what it meant, it is now optional, so you can just ignore it.