Do you have any tips using KDE Connect with a local VPN (Wireguard)? It works great for me on the same network, but unfortunately fails to connect outside of my network despite one (or both) devices connected to my VPN
To sync from android to your PC, you'd need to manually do it by pressing the send clipboard button in the KDE Connect app on your android device. It's due to a limitation imposed by Google. However sync from Linux to android should work automatically. Is that not the case for you?
Oof, I have no experience with (assuming) apple stuff. But it might be even more restricted than android. Good luck and don't forget to share your solution if and when you find it! :)