I don't remember how travel was before 911, but I've had my fair share of airports and International travel after the event.

It goes like this:

Before Covid19

1. Passport/documents check
2. Security check, don't bring guns/bombs/knives
3. Migration check leaving country, check that you have a valid Passport and no restrictions to leave the country.
4. Gate boarding pass check.

Fly through the sky, now at arriving country:

1. Land and leave the plane through gate, no checks.
2. Migration check at arrival country. Checks that you have a valid visa or welcome passport, that you aren't a terrorist.
3. Pick up bags and check with customs that you aren't bringing unwelcome items (food? too much money, illegal goods in the country).

After that, you're inside the arriving country ready to explore.

The most annoying parts were always security check since they can take stuff from your carry on and it's annoying to remove shoes, belts and such, and migrations offices, since they have all the power to capriciously decide not to let you in for undisclosed reasons.

After Covid19

Now that countries know the risks that accepting sick humans can cause to their economy and public health, new restrictions will be added in airports.

At any of the steps at the arriving country they will add a health check. Currently, as a Peruvian I am required to carry my yellow fever vaccination certificate to enter some countries. This list may increase and will get more strict.

Maybe before boarding or before exiting the plane they will add a health check, some quick swabbing, or temperature check, or some internationally accepted official health documentation, that you have valid vaccines and free of any contagious risks.

Obtaining this document, would require that the countries follow some global health standard, and it will be a lot of trouble for visitors from countries that don't comply with the standards to enter the group of countries that do. This may end up as increase of new Visa paperwork per country.

Racism may increase as a result of stigmatizing countries out of the health standards.