If this were the case, then comparable declines should be seen everywhere in the world wherever vaccines were widely deployed. The author offhandedly mentions Germany, without following this line of investigation further other than to provide a link to the author's previous article.
Interesting hypothesis, but a handful of countries is not nearly enough to draw conclusions at this point.
Linking this to vaccines is completely unjustified though. Sad that smart people become so obsessed with wrong ideas.
In many countries, demographics across are skewing towards the older direction and this is likely to cause major issues ib the future
While we are going through alot of cases at the moment, the hospitals are not overwhelmed and people are managing very well. The vast majority of deaths are elderly or people with underlying conditions.
So I wouldn't attribute it solely to lockdowns but mainly to people being too worried to go out and socialize. Lockdowns definitely do play their part. But it's also very expensive to live in Taiwan that having a kid is not something everyone is jumping up and down to do.