It's anything but straightforward.
Ukraine is about 800 miles east-west and 550 north-south; Rammstein's another 800 miles from Kyiv. At Mach 1.2, you're talking about an hour to get to Ukraine and another hour to get to the eastern extent of it, plus the time it takes to go to an in-flight refuelling aircraft multiple times along the way.
It'd be equivalent to trying to establish a no-fly over the whole of Texas, basing out of Chicago, while there are SAM sites in Mexico and California waiting to shoot you out of the sky and aircraft launching missiles from within Mexico with the chance of starting WW3 if you retaliate.
The number of aircraft you'd need would be massive - not just fighters, but AWACS, tankers, search and rescue, you name it. You'd have to have coverage all the way down whatever corridor you were using to get aircraft in and out of the area too.
Now sure, you could (instead of scrambling to intercept) fly combat air patrols over Ukraine and shoot down anything that comes in which might reduce the time-to-intercept to something more acceptable. You still have to cover a massive amount of airspace though!
To be clear, I'm not saying it would be politically easy or low risk. It would almost certainly result in a couple fighter planes being shot down.
> To be clear, I'm not saying it would be politically easy or low risk.
Agreed, I think the biggest issue is the political and strategic risk. In the early days of the war, there was a lot of "it worked for Iraq, just set up a no-fly" chat though.