I am most certain of the opinion that a fairly successful COVID vaccine coupled with a rapid preflight covid test is the answer to resumption of a decent level of air travel
If we can roll out the vaccine we can suppress the pandemic to an insignificant level and remove fear. Testing is not needed. However that needs
1 an ability to vaccinate all countries not just the UK, europe, north america and australasia so there are enough people to fly both ways
2 politicians who can agree a certification system plus relaxation of the lockdowns for vaccinated passengers - not a done deal
3 management of fake news and the anti vaxxing movements
Cynically, 3 is least important as going on yesterday's 120,000 cases in the USA that country will reach herd immunity in April making vaccination unnecessary, but at the loss of so so many lives