When auto-joining networks, macOS and iOS default to the most preferred network, followed by private networks, then public networks.

When your iOS device or your Mac (with macOS Ventura or later) evaluates service set identifiers (SSIDs) and determines which network to auto-join, it tries to connect to networks in this order:

1. Your "most preferred" network

   Known networks are scored based on your actions. If you manually switch to a network, its score increases. If you manually disconnect from a network, its score decreases. The "most preferred" network is the network with the highest score.
    

2. A private network

   Private networks are those set up in homes and offices and can include the Personal Hotspot on your iOS or iPadOS device or your Mac with macOS Ventura or later. macOS Ventura, iOS, or iPadOS reconnects to known private networks in order of most recently joined.
    

3. A public network

   Public networks are designed for general access in public places like a hotel, airport, or coffee shop. Some other examples include Hotspot 2.0, Passpoint, EAP-SIM, or Wi-Fi connections that are provided by cellular carriers and network access providers. 
                   

Your Apple devices prioritize networks by the following criteria, in this order:

1. Configuration method (iOS 16.4, iPadOS 16.4, and macOS Ventura 13.3 or later): Private networks configured using a mobile device management (MDM) profile are preferred over manually joined networks.
2. Highest supported Wi-Fi standard: For example, Wi-Fi 6 networks are preferred over Wi-Fi 5 networks.
3. Frequency band: 6 GHz, then 5 GHz, then 5 GHz (DFS), then 2.4 GHz.
4. Security: WPA Enterprise, then WPA Personal, then WEP.
5. Signal strength.

Unsecured / Open networks will not be auto-joined unless the network was connected to within the past two weeks.