OP has confirmed that they have never been able to connect to this database, so the addition of the package manager is not related.
The connection string being used to attempt to connect to the database is incorrect. See SQL Server connection strings - ConnectionStrings.com
] (search for SQLExpress)
I would expect to see something similar to
"DevConnection": "Server =.\\sqlexpress; AttachDbFilename=C:\MyFolder\MyDataFile.mdf; Database=TiloshDesetDatabase; Trusted_Connection=True; MultipleActiveResultSets=True;"
(replacing C:\MyFolder\MyDataFile.mdf with your own filename)
Further assistance can be found here Troubleshoot connecting to the SQL Server Database Engine - SQL Server | Microsoft Docs