I didn't say governments that are ostensibly leftwing cannot fall into fascism, so can centrist and rightwing governments, rightwing governments being by far and away the most likely.

However fascism is inherently rightwing in a way you can never truly pin on leftism no matter how hard you try to "both sides" this.

Liberal imperialism and fascist imperialism are both murderous criminal enterprises which have and, in the former case, continue to wreak death and destruction on untold millions. It is of cold comfort for an Iraqi orphan to be told that their parents’ killers weren’t “fascists.” Nevertheless, we need to recognize that liberal imperialism and its fascist counterpart operate differently and are vulnerable in different ways.

While both Bush and Obama unquestionably committed atrocities while they stood at the helm of the most powerful capitalist state the world has yet seen, they were not fascists. George W. Bush would be better condemned as a liberal imperialist, one whose speeches were inundated with now-clichéd liberal shibboleths like “liberty” and “freedom.” Admittedly, calling Bush a “liberal imperialist” rather than a fascist lacks a certain punch. But labeling Bush and Obama as fascists doesn’t work because fascism is not only explicitly and emphatically anti-communist, but anti-liberal as well.

In the 20th century, fascism only became a powerful force when liberalism failed.

...

Rejecting both liberalism and socialism, fascism is a set of radical, revolutionary ideologies and political movements of the extreme right that place the nation, however defined, above all other possibilities of human experience and social organization.

https://www.currentaffairs.org/news/2021/06/what-is-fascism-and-why-the-definition-matters