Not if the enemy can get and maintain air superiority. Air superiority closes virtually all room for manoeuvering.
Ukraine's fixed assets were wiped out on day 1, but they have mobile units which I believe are still effective.
The lack of use of a lot of air power by Russia in the last few days I believe is due to the fact that on day 1 they had serious damages and it's just very costly out there.
Mobile AA units can operate independently but I don' know if it's Russian or Western gear, if Russian, it may be hard to replace. Because even free gear from the West right now would require training.
But - there is an unlimited supply of Stingers from the West, and those will do serious damage to all helicopters, and seriously risk close air, and also hugely risk transport aircraft on approach.
Ukraine can plop a 19 year old anywhere within 3-4K of an aerodrome and pluck transports out of the sky with impunity. So far they've knocked out 2 transports which is very expensive to the Russians.
On day 1 they tried to land airborne using 30 transport helicopters, 3 were taken out, that's devastating. Russians had to follow up with 100 helicopter transport landing at once, to land 1000 soldiers, that is a huge portion of their rotary wing assault fleet for one single operation. Very risky.
That said, the Russians are sill flying missions.
But yes, it's a huge factor.
Ukraine's ability to consistently deny Air Support is 100% a decisive issue. Without it, they'd be getting demolished by Russian Airships, much like Iraqi Army facing the US.
'Air Power' is helpful against known targets, in a fight, bombing strategic things like airfields. But even a few dozen migs running daily sorties can't keep 30 Million people down. They can just inflict some pain.
If Ukraine can keep a big plot of territory connected to Europe in it's hands, and conduct operations in occupied lands, it can win.
As of today it's looking bad for Russians. They are not making progress and now the West has been mobilised against them.