Hello Mick,
I understand it can be frustrating when familiar software changes. The Sync button is no longer a standard feature in the latest Windows Media Player versions. It only appears when WMP recognizes a device in MTP or File Transfer mode. If your device isn't recognized this way, the option won't be visible.
I suggest the following: reconnect your device, ensuring it’s set to MTP/File Transfer mode. Check if it appears under the Devices section in WMP. Also, try restarting WMP after disconnecting and reconnecting your device.
If sync is not working, you can still move music manually using File Explorer. Alternatively, options such as MusicBee or MediaMonkey can be used for syncing.
Could you please share the kind of device you are trying to sync to?