Smart TV will not connect to Wi-Fi

Signal strength, password or network compatibility may prevent a connection.

Never open TVs or power supplies. Stop using them if there is a burning smell, smoke or crackling. Do not disconnect power during an update.

Test a phone on the same Wi-Fi beside the TV, with mobile data off. If it is also offline, start with the router guide.
Open the TV network settings, choose your own Wi-Fi and enter the current Wi-Fi password.
Check supported wireless bands in the TV manual. Older models may support only 2.4 GHz.
If possible, test an Ethernet cable between the TV and router. Do not factory-reset the router; record the TV model and exact error if the problem continues.

Test after each step and stop when the issue is solved. Checkmarks are not permanently saved.