Popper's view is neither the last word on what science is, nor the final arbiter as to whether something is scientific: what he did was to add some powerful insights to a description of how science works.
Having said that, it is neither unscientific nor against Popper to postulate something for which there is currently no evidence (the search for exoplanets was started before there was evidence of them) - you would have to postulate something that cannot, in principle, be empirically determined (such as p-zombies) to violate the falsifiability principle (if that's what your specific issue is here.) Such hypotheses are not outside of science; they are an essential part of it, and some unspecified part of scientific spending is effectively spent on generating them.
On the other hand, as Hossenfelder has pointed out [1], falsifiability is a low bar. In the case of shadow life, it is reasonable to ask both how it could remain isolated and why have we not noticed it yet.
Having said that, it is neither unscientific nor against Popper to postulate something for which there is currently no evidence (the search for exoplanets was started before there was evidence of them) - you would have to postulate something that cannot, in principle, be empirically determined (such as p-zombies) to violate the falsifiability principle (if that's what your specific issue is here.) Such hypotheses are not outside of science; they are an essential part of it, and some unspecified part of scientific spending is effectively spent on generating them.
On the other hand, as Hossenfelder has pointed out [1], falsifiability is a low bar. In the case of shadow life, it is reasonable to ask both how it could remain isolated and why have we not noticed it yet.
[1] https://backreaction.blogspot.com/2019/01/just-because-its-f...