C# database classes to change between postgres and SQL Server

Question

I am overthinking this and can't find the right terms to search on in Google.

I have a website that connects to a SQL Server database with mostly centralized classes to call out to the database.

I was able to copy/paste those classes and tweak them to connect to a postgres db by simple changes like changing:

This for connections

SqlConnection connection = new SqlConnection(ConnectionManagerToUse); 
PgSqlConnection connection = new PgSqlConnection(ConnectionManagerToUse);

and this for commands:

SqlCommand SelectDataCommand = new SqlCommand();                        
PgSqlCommand SelectDataCommandPostgres = new PgSqlCommand();

This worked great so far by changing all instances of the above. I want to see if there is a way to have a class or something that is middle man that I can call to change between these 2 in the code so I only have to change code in this middle function to change between Postgres and SQL Server and not everywhere I call out to these commands in my code (obviously specific SQL calls and SQL syntax would be different but I am looking for ways to update the underlying code calling out to the database, not the actual SQL syntax).

Something like the below. I would call this instead of the above (I know this does not work this is just for example) then if I want to change database technology I just change it with a single variable or something in this centralized class/config files (or even have ability to connect to 2 different databases with different technologies at once.

For connections example:

public T GetConnection<T>()
{ 
    if (_DBTechnology == "MSSQL")
    {
        return new SqlConnection(_connectionStringMSSQL);
    }
    else if (_DBTechnology == "POSTGRES")
    {
        return new PgSqlConnection(_connectionStringPostgres));
    }        
}

I know the above is not valid and I have only used generics a few times so this may not be the way to do this at all. So any suggestions would be helpful.