Fronline combat is just a tiny, tiny part of the war effort. In a modern, professional western army, you've got like 8 or 9 non-combat military job for every single combatant. The rest is logistics, medical, logistics, technical, logistics, intelligence, logistics, administrative, and logistics, with a dash of logistics and some additional logistics for good measure. Combatants need food, they need medical care, they need supplies, they need intel, they need communication and coordination. All these non-combat tasks can be accomplished by non-combatants.
This is what happens in every guerilla. In every insurgency. In every resistance. And this is the kind of war Ukraine is fighting.
Civilians are also good at psy-ops. In some of the cities and towns that Russia managed to seize, there were constant protests against their presence. Not fighting. Just people standing on the streets with signs, shouting slogans. No weapon or violence. Seems pointless, but it demoralizes the Russian troops.