For questions like this, you may find 'Help & contact' (top left of your Ebay page useful. If you use 'Simple delivery' as the search term, all the details are there.
You can offer free postage but you will have to pay and you will still have to use Simple Delivery - from 15th, it is mandatory. So, your listings will show 'free postage' but your prices will have to include the cost of Ebay's Simple Delivery. Using free postage is not a way to opt out of Simple Delivery. (I am not sure if you were asking that so apologies if I am stating the obvious.)
From: https://www.ebay.co.uk/help/selling/posting-items/setting-postage-options/simple-delivery?id=5575&st...
If you'd like to offer free postage, go to the 'Who pays?' section and adjust the toggle to select Seller pays. When your buyer completes checkout, you'll be charged for a postage label for a standard delivery service and the cost will be deducted from your account.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)
