How do I remove/delete an offline item

It is my understanding that if 1Password says it's offline, it's actually because it cannot reach the cloud sync servers via network. Your PC doesn't need to be disconnected from the internet to be unable to reach some internet server. There could be many other reasons, most being misconfiguration on the local PC. Security software often interferes, bad name server resolution settings, having both wlan and lan active at the same time, or using a vpn can cause this as well.

So if 1Password is complaining it's offline but you are able to access some internet service and assume you're not offline, you might check everything on the local PC you used to modify network access in some way from the default.