The newest version of the Windows app doesn't support creating or opening local vaults, only storing data in their cloud.
They also no longer offer perpetual/non-subscription licenses, including for the older version that supports local vaults.
At the very least the first would be a requirement for any sort of "self hosted" setup.
I ask because I use iCloud heavily. Nearly 1TB of photos/videos and now use 1Password with iCloud sync.
Has Apple made mistakes when designing iCloud, allowing unauthorized access to accounts? Yes.