Batch Sending
Starting with v6.1, the mobile client is focused on serving the watch and no longer comes standard with picture viewing.
For speed and stability reasons, if you need to transfer a large number of, or FHD pictures at once, it is highly recommended to use a LAN transfer rather than relying on Bluetooth to send them in bulk.

Open any app (system album is recommended), select all the pictures you want to send, click “Share”, and select “Send to Watch” in the pop-up list.

If you cannot find this option, please check if the list is complete and if the current application uses the system’s native sharing interface.