Where in turbotax can I deduct a net loss of $9000 from income due to the sale of a mutual fund?

You enter the sale.  You should have a 1099B for sales.  BUT  If you have a net loss for the year you can only deduct 3,000 (1,500 MFS) max on your tax return.  The rest you have to carryover to next year.  You have to report the carryover every year until it's used up.  You can't skip a year.

Enter a 1099 B under

Federal Taxes on left or Personal (Home & Business)

Wages & Income

Then scroll down to Investments and Savings

Then Stocks, Cryptocurrency, Mutual Funds, Bonds, Other (1099-B) - click Start

Then click Add Investments at the bottom

Next screen hit Continue

Then don't enter or pick a bank, at bottom click on Enter a Different Way

Then pick box Stocks, Bonds, Mutual Funds - then Continue

Enter the bank or broker

Answer some general questions and Continue

Then Continue a couple more screens and you finally get to the 1099B entry screen.