This is true, but not exactly in the way that Tucker Carlson explains. If you are unfamiliar with Tucker Carlson it should be well noted that he is known for his outwardly conservative viewpoint and association with Fox. His history includes a lawsuit regarding defamation in the 2020 election for alleged collusion and fraud against Dominion Voting Systems.
In this video on X, Carlson explains that the Ukrainian government closed elections because they could not win their war against Russia even with Western support such as the U.S. He makes not that we have sent a lot of funding to them to which Carlson does not support nor thinks our country should be due to Ukrainian government corruption.
He then claims that this corruption was noted by an American Journalist, and because Ukraine feared that would discourage western funding, he was killed.
https://www.nytimes.com/2022/03/13/world/europe/brent-renaud-irpin.html
See my issue is that this issue is two years apart, so in total honesty I don't know if they are talking about the same journalist, but these other sources claim that Brent Renaud was in fact killed in the Russian onslaught, and not by Ukraine.
https://www.npr.org/2022/03/13/1086345532/american-journalist-killed-in-ukraine
https://www.cbsnews.com/news/brent-renaud-ukraine-russia-american-journalist-killed/
https://www.cnn.com/2022/03/13/media/russia-ukraine-brent-renaud-death-intl/index.html
Multiple other credible sources state that Brent Renaud was shot in the Russian onslaught that was explained, and not any further conspiracy to which Carlson offers.
The other thing to consider is what Carlson has to gain from this. His media company Fox, is likely in support of not sending allowances to Ukraine for their war, and they do make some very valid claims, but I don't believe that Ukraine would bite the hand that feeds them in this situation, and knowing he has a history of conspiracy and was literally in a lawsuit for accounts of defamation, I think it is safer to side on the case of the multiple other sources that explain a different narrative.
Regardless of what happened may he rest in peace.