When your iPhone won't check for updates, it may be due to network connection issues, system errors, insufficient storage space, or other reasons. Here are some solutions that can help you fix the issue of not being able to check for updates:
Make sure your iPhone is connected to a stable Wi-Fi network with sufficient speed. Try switching to a different Wi-Fi network or restarting your router.
Turn off and restart your iPhone. This can solve many temporary software issues.
Make sure your iPhone has enough space** to update. Head to "Settings> "General" > "iPhone Storage" to check the available space. If you're running out of space, try deleting apps or files you don't need to free up space.
If you can't check the update directly on your iPhone, you can try to use iTunes to update via computer. Connect your iPhone to your computer, open the latest version of iTunes, select your device, and tap "Check for Updates".
Make sure the date and time settings on your iPhone are correct. Go to Settings > General > Date & Time and turn on Set Automatically.
If you suspect that the update is failing due to a problem with your network settings, you can try resetting your network settings. Go to Settings> General> Reset, > Reset Network Settings. Note that this will clear all Wi-Fi networks and passwords, cellular network settings, and previously used VPN and APN settings.
If you're trying to update via cellular data instead of Wi-Fi (not recommended, as the update file can be large), make sure there are no issues with your SIM card and that your data plan allows for enough data** updates.
If none of the above methods solve the problem, it may be a more complex system problem or hardware problem. Contact official Apple support for help.
Before trying these solutions, make sure to back up your iPhone in case you lose data in the process of fixing the problem. Usually, these steps can help fix the problem of not being able to check for updates and allow your iPhone to upgrade to the latest iOS version smoothly.