In first example here:
https://docs.microsoft.com/en-us/dotnet/api/microsoft.azure.cosmos.cosmosclient.getdatabase?view=azure-dotnet

There is a typo:
("myDatabaseId"];

Should be:
("myDatabaseId");

replace bracket with parenthesis.

Document Details

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• ID: 440cc9dd-9e0b-44f8-f31a-36cdd97d5bbd
• Version Independent ID: 1ab2bf08-78df-a6c2-4c11-f021f8942a64
• Content: CosmosClient.GetDatabase(String) Method (Microsoft.Azure.Cosmos) - Azure for .NET Developers
• Content Source: xml/Microsoft.Azure.Cosmos/CosmosClient.xml
• Service: cosmos-db
• GitHub Login: @rloutlaw
• Microsoft Alias: routlaw