COVID lockdowns weren't sustainable and while they reduced pollution to some extent they didn't come close to eliminating it. Like in my country we turned off coal, but only because we don't have much coal to begin with. We were still using plenty of gas power, as that's our second largest energy source. Here in the UK our largest energy source is Wind, and we aren't even doing that well compared to France or Spain on the energy front.
Things also still got manufactured and sold, and that's where a lot of pollution comes from. Food and goods production. Eliminating transport pollution would help for sure, but it's like 14% of the problem. Electricity generation, heating, and agriculture are the things we need to fix the most. Fixing electricity generation would also help with transport emissions as we could use more electric vehicles and trains.