Thank you for your asking. Kindly provide the information below so that we can better assist you.
1. Please try reset Network: Settings>System>Advanced>Reset options>Reset Wi-Fi, mobile & Bluetooth
2. Does the SIM Signal perform well? Only the Wi-Fi encounter this issue?
3. Did the issue appear right after the firmware update?
4. Can the device work with the same router before the firmware update?
5. The router models, which the device could link with perfectly before.
6. Please try SMMI test
Calculator> type ".12345+=">SMMI TEST>Single Test>Wi-Fi Test
If the SMMI test fails, kindly bring your device to the Repair Center for device checking.