Why does TLS1.2 break connections to SQL Server?

I have a Client who moved to TLS 1.2, which broke an app that connects to SQL Server 2017 and it got dumped on my lap. Being a Linux person all I can say is when they went back to TLS 1.1 it worked and here is the only error message I can glean in all this mess: > dbnetlib connectionopen secdoclienthandshake ssl security error When I try to connect to the SQL Server from SQL Server Management Studio, I get this error message: > Error connecting to 'hostname'. > > Login failed for user 'CORP\myaccount'. (.Net SqlClient Data Provider) > > Server Name: hostname > Error Number: 18456 > Severity: 14 > State: 1 > Line Number: 65536 > > Program Location: > > at System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity, SqlConnectionString connectionOptions, SqlCredential credential, Object providerInfo, String newPassword, SecureString newSecurePassword, Boolean redirectedUserInstance, SqlConnectionString userConnectionOptions, SessionData reconnectSessionData, DbConnectionPool pool, String accessToken, Boolean applyTransientFaultHandling, SqlAuthenticationProviderManager sqlAuthProviderManager) > at System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection, DbConnectionOptions userOptions) > at System.Data.ProviderBase.DbConnectionFactory.CreateNonPooledConnection(DbConnection owningConnection, DbConnectionPoolGroup poolGroup, DbConnectionOptions userOptions) > at System.Data.ProviderBase.DbConnectionFactory.TryGetConnection(DbConnection owningConnection, TaskCompletionSource\`1 retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, DbConnectionInternal& connection) > at System.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource\`1 retry, DbConnectionOptions userOptions) > at System.Data.ProviderBase.DbConnectionClosed.TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource\`1 retry, DbConnectionOptions userOptions) > at System.Data.SqlClient.SqlConnection.TryOpenInner(TaskCompletionSource\`1 retry) > at System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource\`1 retry) > at System.Data.SqlClient.SqlConnection.Open() > at Microsoft.SqlServer.Management.SqlStudio.Explorer.ObjectExplorerService.ValidateConnection(UIConnectionInfo ci, IServerType server) > at Microsoft.SqlServer.Management.SqlStudio.Explorer.ObjectExplorerService.ConnectToServer(UIConnectionInfo connectionInfo, IDbConnection liveConnection, Boolean validateConnection) TLS 1.2 was enabled on the server that hosts SQL Server.