The new, but announced policy, reversed Biden's approval for such strikes he made late in his final year in office. Only a few days ago, Trump posted on Truth Social that it was Biden's fault for dragging his feet:

“It is very hard, if not impossible, to win a war without attacking an invaders country. It’s like a great team in sports that has a fantastic defense, but is not allowed to play offense. There is no chance of winning! It is like that with Ukraine and Russia. Crooked and grossly incompetent Joe Biden would not let Ukraine FIGHT BACK, only DEFEND. How did that work out? Regardless, this is a war that would have NEVER happened if I were President – ZERO CHANCE. Interesting times ahead!!!” He then gave Russia its obligatory two weeks to respond.

As always, pay attention to what Trump does, not what he says.

Source: Wall Street Journal

WASHINGTON—The Pentagon has for months been blocking Ukraine’s use of long-range missiles to strike inside Russia, U.S. officials said, limiting Kyiv from employing a powerful weapon in its fight against Moscow’s invasion.

A high-level Defense Department approval procedure, which hasn’t been announced, has prevented Ukraine from firing any U.S.-made long-range Army Tactical Missile Systems, or ATACMS, against targets in Russia since late spring, the officials said. On at least one occasion, Ukraine sought to use ATACMS against a target on Russian territory but was rejected, two officials said.

The U.S. veto of long-range strikes has restricted Ukraine’s military operations as the White House has sought to woo the Kremlin into beginning peace talks.
Elbridge Colby, the Pentagon’s undersecretary for policy, developed the “review mechanism” to decide on Kyiv’s requests to fire long-range U.S.-made weapons as well as those provided to Ukraine by European allies that rely on American intelligence and components.

The review gives Defense Secretary Pete Hegseth final say over whether Ukraine can employ the ATACMS, which have a range of nearly 190 miles, to strike Russia.

And the policy also applies to the British and French Storm Shadows.

The Pentagon review procedure also applies to Ukraine’s use of the Storm Shadow as it relies on U.S. targeting data, according to two U.S. officials and a British official. The U.K. government declined to comment.

And it also applies to American-made missiles sold to European countries in support of Ukraine.

The administration this past week approved the sale of 3,350 Extended Range Attack Munition air-launched missiles, or ERAMs, which are set to arrive in Ukraine in about six weeks, two U.S. officials said. The $850 million arms package, mostly funded by European nations and which includes other items, was delayed until after Trump’s summits with Putin and Ukrainian President Volodymyr Zelensky.

Several U.S. officials said use of the ERAM, with a range between 150-280 miles, would require Ukraine to seek approval from the Pentagon. The State Department didn’t respond to a request for comment.

As one can imagine, there are issues when you're at war and have to run your plans by the United States first, not only operationally but also for security purposes.