SSMS18 How to connect to a local server?

I've been working on SSMS18 for the longest time, but I'm mostly connecting to a remote SQL server. But now I'm trying to connect to my localhost server but it's just now that I can't connect.

I've already searched some tips online but nothing seems working and most cases use outdated SSMS server.

TITLE: Connect to Server
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Cannot connect to localhost\sqlexpress.

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ADDITIONAL INFORMATION:

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified) (Microsoft SQL Server, Error: -1)

For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft%20SQL%20Server&EvtSrc=MSSQLServer&EvtID=-1&LinkId=20476

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BUTTONS:

OK
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Open SSMS then press Connect, and for the Server Name type: (LocalDb)\MSSQLLocalDB, keeping authentication as Windows Authentication.