Although that's true, there's a lot more to a human than their ability to adapt, they have relationships with other people (depends on the character), relationship with inanimate objects they use daily; like phones, internet, Google (except tragically abused or closed off people), cultural relations; like how their senses got used to certain scents and noise in their daily life.
Cmiiw but it rarely happens that humans and their senses (organs and what not) adapt to a new environment in less than 24 hours, take flights for example; they take a toll on the body (jet lag, time differences, sickness). I think OP is referencing to those aspects. On the other hand, we as readers don't really know for sure because it involves all these theories like mana and does our "soul" adapt quicker because it's in another body that's already accustomed to the world but that then spirals into the argument of what our "soul" does and remembers, are we just a lump of fat having vivid hallucinations or are we spiritual beings at core?
TL;DR idk man believe what you wanna believe, I personally won't let this affect my reading experience bc I'm reading for fun not for an identity crisis (ʘᴗʘ✿)

Is it just me or do these reincarnated MCs adapt wayyyyyyy too quickly. Like gurl wdym u literally died and now uve possessed a body that you are not familiar with in an unfamiliar era/world AND U JUST ACCEPT IT??!? like most stories ive read(there are some exceptions)have the mc be like "wait a minute this isnt my body.....OH NO I VE POSSED XXXX CHARACTER FROM XXXX NOVEL....oh well guess i better go do something useless ..." like no i would be freaking out in a body that i dont own and in place where i have no knowledge of ┗( T﹏T )┛but well this is just my opinion lol