Russia and Belarus make money from the planes flying over their airspace. They won't be collecting that money so there is at least one consequence.
Some countries go above and beyond; Russia typically grants overflight access to one airline per country, so SAS has the ability to fly over Russia while Norwegian Air never has.
In any case grandparent poster is probably just repeating info out of this video: https://www.youtube.com/watch?v=jdNDYBt9e_U&t=382s