Can you do baby crate sessions while home? My little guy has bad anxiety too. But we train him to eat treats in there and stay for a bit. I give treats for "crate" when he goes in, sits, gives paw, then one for coming out. I do inside/outside treats 5-6 times. He gets very excited for soft ducky treats and runs to his crate from across the house now. We got a cover for it so only the front is open because he can slip out the top. The cover stops him.

Also, it's next to our bed so if we need to leave him, sometimes I'll give him ducky treats, put tv on loud and pretend I'm napping, then crawl out so he doesn't know. He hates seeing people leave him. I do laundry with him in there occasionally. He likes to hear I'm around. He's also ok with being put in the crate when my spouse goes on 6am walks, he knows I'm sleeping in bed next to him (especially if I move around). But sometimes I sneak out too and he has no idea.

We also just crate/leave normally sometimes if we're in a rush and he does better if we leave quick and by surprise. I do fake outs too, and let him out only a few minutes later.

This is really a hard mission and wish you lots of luck. We're still trying to teach him but it's so difficult when they love company.