Air travel might be allowed in that flights happen, but the second travelers land they are immediately sent into quarantine in some countries. Poland, for instance, requires 10-day quarantine for anyone flying into the country, even from other EU states. That quarantine is checked by requiring you to install a mandatory phone app and also by sending the police around to your address.

Also, because some EU countries are claiming that crossing their borders is only allowed for essential reasons proven by documentation, the airport in the country of origin will prevent many people from even being able to board the plane in the first place.

Air travel worldwide is just fine. In airport transit zones all you need is a mask.

We flew from Northern Europe to South Asia a week ago and the flights were filled 60-70%.

Absolutely false. I am not saying airports are a source of infection. What I am pointing out is that air travel is allowing for all these variants to propagate to new populations.

The pervasiveness of the UK variant in Europe would have been contained or at least decelerated with travel restrictions.

A living proof of this is both New Zealand and Australia. These countries still allowed for sea and air freight but banned travel. Both countries are roughly back to normal life, while we in Europe are still trying to blame pharmaceutical manufacturing vaccine output, as if that is the sole cause of our problems.