Well, the more precise phrase would be "fertility decline was not caused by the invention of new birth control technologies". It is totally possible for a society to have below replacement fertility using only birth control methods available since pre-industrial era.

If birth control hasn’t been enabling fertility rates to decline, then what has? Rising women status contributed more than everything else combined.

However, the increasing availability of the birth control pill, other contraception methods, and the legalization of abortion during the 60s and 70s (in the US) are notable >for contributing to the declining fertility rates in the US. That was a continuation of trend which started more than a century before that, after temporary baby boom reversal ended.

No, the opposite doesn’t usually happen. For all of human history, higher fertility memes have tended to outlast lower fertility memes. Now of course, the last 200 years are exceptional, since many lower fertility memes have overpowered higher fertility memes. The reason that happened is that communication became much easier. So it is reasonable to expect that low fertility memes will generally win for as long as the world remains interconnected.

there’s also many high fertility memes and memeplexes that still have very high fertility rates, such as the fundamentalist Muslims, the Amish, and Ultra-Orthodox Jews. There were many more highly religious (and fertile) communities in the past. So the default is to expect that they will follow the same path like say Quebec.

I’ve written a list of things that could be done to boost Western fertility rates. This list looks rather US-centric. Many countries, for example in eastern Europe don't have these specific problems but have low fertility anyway. So most likely this would not help much.

There are several dubious assumptions there.

The first is that fertility decline is caused mostly by birth control. The problem is, it began long before birth control became widespread. A century ago, most developed nations had TFR somewhere between 2 and 2.5.

The second is that high fertility memes are durable. But usually exactly the opposite happens, "cultural change causes lower fertility" is the same as "high fertility memes lose". That happens with religious groups the same way - Mormons used to have much higher fertility, and now they don't.

As for adapting for deceases - that is a survivor bias. For example, several dozen amphibian species are believed to be wiped out by fungal infection in last decades. It is rather unlikely that humanity will go extinct that way, if anything there are some isolated tribes. But industrial civilization can collapse due to low population long before natural selection would cause fertility to rise again. With TFR 1.2 (like in Italy now) population would drop below 100 million in about three centuries.

 Anti tank FPV drones? Almost certainly not long term as they’re more expensive than ATGMs,

That is not true at all, anti-tank fpv cost is about 1/100 of a Javelin missile. It is not obvious how much autonomous guidance would add to a drone cost, but probably less than 10000%.

The point about chaff is that a regular size sniper rifle bullet can't contain it in any significant quantity. Smalest existing chaff shells are for 23mm cannons, and a drone carrying ~20mm cannon has to be rather large.

In general, lessons from the Russo-Ukrainian war are not very relevant for a "state of the art" conflict, because both sides have weak air forces. It is like watching two armies fighting with bayonets because they are out of ammo and concluding that you should arm your soldiers with swords and shields.

Also, this makes many assumptions which are dubious (like, sniper drones aren't anywhere close to practical use, and it is not clear if they are viable), but also some which are strictly false:

1. Bullets can't carry enough chaff to "surround" a tank
2. Lasers can destroy artillery shells (which are made of steel) in flight, there is no practical way to harden a light drone against them.

I disagree that "forever is really long time" in this context. To delay AI forever requires delaying it until industrial civilization collapse (from resource depletion or whatever other reason). That means 200-300 years, more likely that 50000.

Again, that some estimates are given in papers doesn't mean they are even roughly correct. But if they are - then no, that scenario is not suicide. There are some nations now which have lower GDP per capita than USA had two centuries ago.

As for defense - well, that definitely wouldn't be a problem. Who and why will be willing to invade a big and very poor country, leaders of which claim they still have some nukes in reserve?