A) I do t know the relation to the death rate, but before the decline, the birth rate was very clearly higher than the death rate. If the 20% decline caused it to equal or drop below the death rate, then see B). But if the birth rate got closer to the death rate, yet is still higher, then population will continue to increase. However, it will increase at a slower rate.

B) any decrease in population is unlikely to be felt until 18-25 years later. Until then, those children are still mostly just following their parents around or perhaps are in college which is almost like its own little contained ecosystem. You are unlikely to feel like they are making things more crowded. During that 10-25 years, there are children born during the faster birth rate time who are becoming adults and entering the world, making it seem more crowded.

C) I would be very doubtful of any study that asks people if it "seems more crowded" right now for several reasons. Mostly, we just got out of a global pandemic that held our country in grip for nearly 2 years. Maybe you weren't isolating, but a huge percent of the population were. So you are definitely experiencing a surge in people going out in public. You may think it seems more crowded than before the pandemic, but it's so hard to overcome implicit bias in the way we perceive the world. That's why rigorously controlled studies are required. We need to know how many people trafficked a certain area in. A certain time 3 years ago, and we need to average over several days of the week because their schedules and hobbies and reasons for going outside are not only dependent on that, but may have changed in the last 3 years. We should probably even consider time of year. We went into the pandemic during winter, and really this spring and summer was when the majority of people I knew started going back to life as it was before (more or less). So the study should either average across multiple times throughout the year, or track month, temperature, weather, and all factors to make sure they aren't affecting the number of people that are out and about. Your brain does not do any of this automatically. I am highly suspicious that your anecdotal evidence actually implies things are more crowded. In fact, I even sorta agree with you, I never seemed to have to wait for the self-checkout at Walmart but maybe 2 or 3 times a year at the worst. Now it seems like I'm waiting more often than not. I thought that was weird until I realized I also just moved from a city of 75k to over 400k. Maybe waiting is more common here. Maybe people are less likely to choose the person operated checkout because they're so use to isolating, they're not used to interacting. Maybe Walmart has fewer people on duty to checkout either due to the pandemic itself or to keep pace with consumers, but they haven't yet bounced back fully. There are so many variables.