Perhaps it's the proliferation of new-imperialist views that's the root cause of the support for war.  Searching for news I came across a Trotskyist newspaper where I found the following statement:

"As we state in the draft resolution, the imperialist war against Russia in Ukraine marks the opening stage of a new imperialist re-division of the world. In the most profound sense of the term, this war is an outcome of the unfinished twentieth century. Our opposition to this imperialist war as well as the capitalist Putin regime is rooted in a historical understanding of the entire 20th century and the struggle of the Trotskyist movement against Stalinism."

I'm not a Trotskyist or a Bolshevik but having grown up in Soviet Union, I agree with this statement.  And weather it's a relic of the 20th century or a sign of things to come, the World Socialist Web Site is reporting organization of youth rallies throughout the world (primarily in the countries where Socialist Equality Party is active):

https://www.wsws.org/en/articles/2022/11/04/pers-n04.html
https://www.wsws.org/en/articles/2022/12/07/syln-d07.html
https://www.wsws.org/en/articles/2022/12/08/iyss-d08.html
https://www.wsws.org/en/articles/2022/12/09/akmv-d09.html
https://www.wsws.org/en/articles/2022/12/09/fqhf-d09.html
https://www.wsws.org/en/articles/2022/12/09/kflp-d09.html

To understand where they are coming from, I found this article instrumental to understanding Trotskyist view on the roots of the war:

https://www.wsws.org/en/articles/2022/10/18/prin-o18.html

I would add that Ukraine had it's own anarcho-communist leaders (though not strong in theory but very prolific in actions and still popular):

https://en.wikipedia.org/wiki/Nestor_Makhno

And if you've never heard of Trotskyism, here is an article that explains the differences between various socialist movements:

https://paradoxoftheday.com/differences-between-marxism-leninism-trotskyism-stalinism-and-maoism/