Since you like the default names, try entering the default name assigned as your custom name. I changed my ATV 4K name to "ATV 4K 2017", not sure what the default was. I entered "HomePod mini" for it, again not sure what the default name was. If you have multiple devices of the same kind, for example multiple HomePod minis, it makes since to give each a unique name, otherwise you might get confused about which one the name refers to. The system will know though since it can look at the serial numbers, but it might not be so easy for you to know exactly which HomePod mini you select in Home app if they all have the same name.