The usual reason for the qualified business income (QBI) deduction mysteriously showing up on your tax return is that you have an amount in box 5 of a 1099-DIV (Section 199A dividends).
This is income from REITs (Real estate investment trusts). Your mutual fund has holdings (investments) in REITs. It qualifies for the QBI deduction. Don't try to remove.
The alternative is delete the box 5 amount at the 1099-DIV screen. The amount is already included in box1, so it gets reported and taxed, even if your remove it from box 5.
