Help with new dog.

Hi everyone, I recently adopted a 1 year old German Shepherd/Red Heeler mix through a "live at home" volunteer foster program, and I have had him for about a week now (I am also a newish dog owner, had them in the past but never my own dog at my own place)

Overall hes been great already kennel trained, potty trained, and doesnt bark at all. My main concern is his confidence. He's extremely shut down and I'm not sure how to help him come out of his shell.

He rarely leaves his kennel on his own, and when I put his leash on to go outside he pancakes completely and wont move. After a full week I feel like we should be seeing at least some small signs of progress, but honestly I feel like we're at a standstill.

I understand he needs time to decompress and adjust to a new environment, but Im starting to wonder if there is something more going on. I have run out of ideas and could really use some guidance from people who have been through something similar.

Any advice would be greatly appreciated, Thanks

P.S. I want to mention that I'm not just looking for a pet to have around the house Im looking for a capable companion. Someone I can train to a high level, bring everywhere with me, and have truly by my side day in and day out. Both the GSD and Heeler in him have incredible potential for exactly that, which is part of why I chose him. I just want to make sure I'm setting him up for success and not missing something early on that could hold him back down the road.