

This happens on slower USB devices the data is buffered and the write won’t be complete right away. You can use the “sync” command and wait until it completes to make sure it’s done before you unmount the device. These days KDE shouldn’t let you unmount before it’s done though.
It’s perfectly fine to host jellyfin online. Use a proxy server to enable TLS and do not use default ports 80/443. Use letsencrypt for free certificates. No need for VPN to access here either. Do not expose any other ports such as SSH on default ports. Lock down your jellyfin server and any other related services behind a VPN service and block access to Internet through other interfaces (except for port forwards on your ISP for jelly). Go high on port ranges since they typically aren’t scanned or blocked. Go dual stack for best results and don’t use your router address for IPv6 more than likely you have your own /64 choose a different address for port forwards. Do not assign this address to your internal servers. Use a reserved unrouted IPv6 range internally and do NAT6. Do not allow any raw IPv6 internet access