Thunderbolt Display working intermittently with my MacBook Pro

I have one of the last Intel MacBook Pros and plug it in via USB-C to my (now discontinued) Thunderbolt Display. It has worked brilliantly for several years until just recently. The Thunderbolt Display seems most of the time to require the lid of the Macbook pro to be up for it to be powered.

I have the display setting to 'Mirror for Thunderbolt Display'.

I'm running Sonoma 14.2.1

As I say the problem is intermittent, when I return from a trip for a few days I have the problem and then as if by magic, it all settles down and I can leave the MacBook Pro lid down and all is fine. But for now, it's unsettled and intermittent as I just returned from a trip.