A1550 is the iPad mini 4
Apple lists it as the Wi-Fi + Cellular model. This is the version sold in Australia.
For your iPad mini 4
Not sure what’s wrong with it? Diagnostics at Riverwood Plaza are free.
Software updates
Stopped at iPadOS 15
No. The iPad mini 4’s last major update is iPadOS 15. Apple may still send security fixes for iPadOS 15, but it won’t get iPadOS 27 and newer apps will gradually stop supporting it.
Other iPad mini 4 model numbers
Check it yourself
Where to find the model number.
Settings → General → About, then tap the Model Number line once to switch from the part number to the A number. On most iPads it’s also printed on the back. Got a different number? Look it up here.
Cracked iPad mini 4? Bring it in.
iPad screens, batteries and charging ports at Riverwood Plaza. Free diagnostic, no obligation.