The iPhone 8 plus is connected to wifi but cannot access the Internet, while other devices connected to the same wifi can access the Internet, the following reasons may be possible:
The network Settings of the iPhone 8 plus are incorrect. It is recommended to try to restore the network Settings, the steps are as follows: Go to Settings > General Purpose > Reduction > Restore network Settings.
Wi-Fi router problem. Try restarting the router or resetting it.
If you can, try connecting to another Wi-Fi network to see if you can get online.
Carrier network problems. If other devices also fail to access the Internet, the carrier network may be faulty. Contact the carrier.
System problem. If the phone system version is not the latest, it is recommended to upgrade to the latest version.
If the above methods do not solve the problem, it is recommended to consult Apple after-sales or professional help for more professional help.
Because the 8p network signal reception configuration is not as good as other mobile phones, you must have a strong signal to connect.