You're trying to compare apples to hand grenades.
Ukraine, a second world industrial nation which under the right circumstances could emerge as a productive and technologically advanced nation in the way Poland, Latvia, Hungary, etc. did.
Yemen, a terrorist shithole of a country that has oil wealth but is utterly backwards and embraces the death cult of Islam.
Ukraine has energy reserves that Russia lusts after. Ukraine is peopled by ethnic Russians, since Stalin engaged in genocide and murdered all the ethnic Ukrainians in the 1920's. Hence Russia justifies their invasion based on the idea that they have a "right" to Ukraine since it is peopled by Russians.
Yemen is a terrorist shithole that keeps attacking their neighbors, most particularly Saudi Arabia.
Ukraine is sympathetic - Yemen is a terrorist shithole.