Struggling with leaving him alone

My partner and I have been lucky enough to bring a beautiful standard wirehaired dachshund into our home (we brought him home at 10 weeks and he’s currently 18 weeks). Not going to lie, it’s been a challenge so far and we’ve had many stressors that we’re all working through but our love for him grows everyday. He’s generally a really good pup, likes his food, will sleep, is getting the hang of toilet training, enjoys vet visits and all in all has a wonderful temperament.

Our main issue at the moment (other than basic training which is taking its time) is that our pup just hates being left alone. He’ll sleep in his crate perfectly during the night, getting up only for a toilet break and settling back down. But if we try to put him in it and get anything done during the day? Impossible. I’m feeling stuck as I work from home often and when I’m not at home my partner is, which we know could be creating the issue. It’s just impossible to go about normal daily life when he needs to sleep. A tiny sound when he’s sleeping and that’s it, he’s awake and crying to be let out/with us (except he’s never slept in his crate during the day as we’ve never had success). We’ve been building his relationship with his crate by feeding kongs and long lasting treats in there but he struggles to settle down for a nap unless he’s with us, which is causing problems. He just continuously winds himself up until he’s getting zoomies and never settles down.

I’m really worried about creating any potential separation anxiety behaviours with him, ultimately wanting the best for him but selfishly I’d also like to be able to run to the coffee shop on my own every now and again. Right now, that seems like it will be an impossible task.

For context, we also live in a flat and need to be mindful of neighbours who we have told we have a puppy so they know, he’s generally fine noise-wise but really sounds alarms the second he’s left.

I think what I’m looking for here is anybody else who’s had a similar situation, to hopefully tell me is does get better or that some silver lining is around the corner. I don’t want him stressed if we’re out of sight, or if we need to leave him for a little while and I’m feeling like I’m failing him right now.