Enco, agency, free will and similar notions are not part of Lama. It is as i indicated inheritability of acquired characteristics. In both instances when pondering Lamarck and Darwin change or evolution is dependent on individuals.
I think you misread the giraffe example. There is no disputing that forbears of modern giraffes had shorter necks. The issue is how did that come about. The accepted science is through natural selection. Even after the revitilazation of Lamarck as a possible partial explanation for evolution the long neck of a giraffe is credited to natural selection.
There is no denying the inheritability of epigenetic changes. It is documented and generally accepted. Dutch hunger winter of 1944 is one example. Pregnant Jewish women during holocaust hiding from Germans is another. Thing is mammals have a “reset mechanism” that causes the inheritance of those changes to fade in just a few generations. More primitive creatures like C elegans the epigenetic changes last many more generations.
There is also a (forgot the title) biological mechanism in which beneficial epigenetic changes produce mutations that capture the beneficial epigenetic change. It is likely that Lamarck’s inheritability of acquired was more in play for earliest evolution. Keep in mind the knowledge of genetics when Lamarck was working fell far short of today’s knowledge. Lamarck’s ideas have been substantiated. Teh sowmehow is replaced with know how. The issue is its role in evolution if any. Also keep in mind as a discredited scientific concept scientists for decades avoided it like the plague. Therefore our purview is limited. Sort of parallel to the criminilization of marijuana.
Oh and as an aside there is documentation apart from microbes of insanely fast evolution. Moths during industrial revolution when trees turned black due to pollution made white moths targets. Selection pressure caused very rapid response and produced black moths. There are others as well.
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