Since you are focusing on iOS in your question, I can recommend looking at
Apple's Bluetooth Developer Web Site.
Take a closer look at Bluetooth profiles that iOS and iPadOS support
And Chapter 15 of Accessory Design Guidelines
From personal experience, I would recommend using an Espressif ESP32 as a development standin for your thingy, as you can learn a ...
Adding to hardillb's answer... I don't know exactly what device you have, but you could consider the simple workaround of an external keyboard. If your devices have USB / microUSB port, you can get a single keyboard relatively cheap that you can plug in long enough to set up the WiFi connection.
If the devices don't have USB, you could also attempt pairing ...
Yes, it's a perfectly valid approach that is used by many different IoT devices.
One I've implemented more than once, bur here is an example that uses WebBluetooth so you don't even need a native client on the phone/laptop (but you do need Chrome)