A lots has changed. There were major 2018 Federal tax change revisions, and a number of new IRS schedules as a result. TT Free is for simple returns. If yours now requires any of those new schedules, you must upgrade to a paid version.
Also, for those reading: "Nothing has changed" isn't strictly true. We are all a year older, and some deductions/credits have age limits that can impact your tax return (but not necessarily the TT fees).