Trump said repeatedly before and after the election that his tax returns would eventually be released, but couldn’t because they were under perpetual audit. Being under audit does not deny one the ability to share them.

After the House subpoenaed his financial records from the IRS, Treasury Secretary Steven Mnuchin defied the subpoena.

Trump filed suits against the US House Ways and Means Committee and the state of New York to prevent his taxes from being obtained. His legal team’s contention was that a sitting president enjoys “absolute immunity from criminal process of any kind.”

After being stuck in appeals, the Supreme Court decided to review both legal cases, Trump v. Mazars US, LLP and Trump v. Deutsche Bank AG. A decision is still pending.

The Wall Street Journal – Trump Sues House Panel, New York Officials to Protect State Tax Returns
The New York Times – Trump Taxes: President Ordered to Turn Over Returns to Manhattan D.A.
The Hill – Judge puts new hold on Democrats’ lawsuit seeking Trump tax returns
The New York Times – Supreme Court to Rule on Release of Trump’s Financial Records
Wikipedia – Tax returns of Donald Trump