If you have them linked to TP-Link cloud via Kasa Mobile App, then they’re commissioned to the cloud. This is where the confusion sets in.
HA has a native TP-Link core integration. But you won’t use it if you’re trying to add them as Matter devices. The devices themselves (and the boxes they came in) will have a QR code (and under it, typically a PIN code). That’s what you will use to add them as Matter devices. You’ll need the Matter Server App installed in HA, then use “Add Matter device” on the integration page.
Otherwise, if you’re adding them to HA using the TP-Link core integration, then they’ll be tied to the cloud and phone home whenever they desire, unless you use python-kasa to commission them locally.
I’m not 100% sure, but if they’re giving you any complications adding them as Matter devices, I would assume it’s because you didn’t install the Matter Server App -or- you already added them to the cloud using the Kasa Mobile App. Me, personally, I would decommission (remove) them from the cloud (app), reset the devices to factory, and add them strictly to HA via Matter.