For a Private seller, only certain items, for example very lightweight or overweight items, are exempt from Simple Delivery.
As a Private seller you should be using, eBay wish you to use SD.
You can still use your own postage, but you cannot then add tracking, and your payouts for those items will be held for a minimum of 14 days.
Whilst not without its faults, it does have big advantages you may not be aware of.
Using SD if an item is lost or arrives damaged in the post, eBay pay for that full refund to the buyer, and you keep the whole payout.
This link describes the workings of Simple Delivery, worth reading before you make a decision not to use it.
https://www.ebay.co.uk/sellercentre/postage/simple-delivery?mkevt=1&mkpid=2&emsid=0&mkcid=8&bu=43952...
@davycr-51