But it is likely that the cumulative experience of the pandemic -- including psychological stress, social isolation, disruptions in daily life, reduced activity and wellness -- contributed to the observed changes...
My brain have have reversed in age during the pandemic:
1) Psychological stress. I have never been happier in my entire adult life as I was during the pandemic. Working from home became the accepted norm. I didn't have to deal with shitty workplace offices (they are all shitty, without exception). I got to watch my kids grow, rather than only witnessing a small sliver of it. My wife and I got much more time with each other, which let us bond more than we had ever been able to bond in the past. Online shopping became the norm, etc. My stress level went down by an order of magnitude. My entire family got COVID, were bed-ridden for a day or two, then recovered like nothing happened. I hadn't slept that well in years, and my wife and I were supposed to be in the high-risk of death category. The pandemic years were the best years of my entire adult life, and they ended all too soon.
2) Social isolation: I was able to get away from people in general. Talk about mental rejuvenation! I had my wife and kids with me, which is all the socialization I need and want. I had the Internet for entertainment and education, and whatever socialization I wanted. Better yet, I could end socialization as needed and wanted. I was able to measure out what little socialization I wanted, and end it when I had enough. It was great.
3) Disruptions In Daily Life: Daily life requires all the things I don't want, so changing it was highly welcome. My stress level (and blood pressure) went way down during the pandemic. The worse part of the disruption was when it ended. Going back to daily life has raised my stress level (and my blood pressure) again.
4) Reduced Activity And Wellness: I lost 40 pounds during the pandemic due to increased and regular exercise, and due to greatly reduced stress. My blood pressure went down, my bonding with my family increased, and every metric of wellness I can think of improved (including my blood lipids). They were the golden years of middle-aged wellness.
If these are the markers for brain aging, my brain must have reversed aging by a few years. Bring on the next pandemic!