Good pay, ownership/responsibility/autonomy in work, and a willingness to fire people who aren't a good fit.

In my experience, if you can hire competent, well-rounded people, and give them ownership of their work, a decent culture will emerge which can then be fostered/guided. You won't hire/retain those people without good pay.

Conversely, if you hire scrubs, or unbalanced people, and then are reluctant to fire them, you're screwed. That sycophant that shows up but doesn't follow instructions and does the bare minimum? The 10x dev with no empathy or social skills? They're poisoning the well day after day.

Have an annual company off-site that doesn't suck, is about all that's needed to develop/maintain bonds IMO.

Also, remote work isn't for everyone. Some people just have no self-control, and will watch youtube all day instead of working. Basic management and tools should expose people who just aren't contributing much. They might be great people otherwise, but still need to be fired.