OK. Let me phrase again:
Power is key military infrastructure used to run military command centers, radars, etc. Civilians can survive with candles, water tablets and canned food. Power plants are minimally staffed. Disabling them does not harm civilian lives. Not war crime.
Oil is key military infrastructure used to fuel military vehicles. Civilians can walk or ride bikes. Oil refineries are minimally staffed. Disabling them does not harm civilian lives. Not war crime.
Bridges are key military infrastructure for transporting ground force vehicles and logistics train. Civilians can climb mountains or swim. Bridges do not have staff. Disabling them does not harm civilian lives. Not war crime.
Semiconductor fabs are key military infrastructure for building chips for electronics used in military vehicles and research. Note that this is a US definition that they used to put SMIC on the entity list as a "military end user". They are minimally staffed at night and are highly automated. Civilians don't need smartphones to live, nobody said smartphones are a human right. Not war crime.
Hmm it seems like all my proposed targets are legal. They aren't pure civil infrastructure, they're actually military infrastructure with some certain civilian uses.