Astronomy papers like this are pure science fiction. It's fun to think about but this is pure extrapolation and does not follow any scientific method. The only way to scientifically prove these things in this paper is to get first-hand measurements, which are impossible with today's technology.

I understand what you’re saying, but the paper ends with a two-page section (4.4) on “Observational Prospects,” including possible biomarkers. It seems like if nothing else, the point is to not rule out such worlds in the search for extraterrestrial life (including intelligent life).

I'm not so sure about that. People understand the structures of stars very well, the same methods ought to work for planets, at least somewhat. Going there looks very hard but remote observations are rapidly improving.

What is your point? Do you think others will be misled?

It's not science fiction, it's the first step of science itself.

You can't justify doing any kind of basic research without some sort of theory or question or simple academic interest. Even basic undirected research isn't utterly random. Someone has to have some sort of idea they want to investigate. "Is it possible that there might be other environments similar enough to our own that they might be inhabited, or habitable, by anything, not necessarily us nor excluding us?" is no more or less a basis for science than say documenting the funny structure of the powder/scales on butterfly wings, initially just because someone finds it interesting, but of course everything, including that, ends up being useful and valuable sooner or later.

It IS fun to think about, but this is not a crime, or even merely silly or pointless, and wasn't at any time let alone "with todays technology".

For others wondering about the term 'Hycean':

The OP authors tell us (p.1),

A new type of habitable exoplanet within the sub-Neptune regime was recently proposed by Madhusudhan et al. (2021), known as Hycean worlds.

Madhusudhan et al. 2021 [0] tell us (p.3),

... in this study we focus on planets that allow for large oceans with habitable conditions underneath H2 -rich atmospheres. We refer to such planets as "Hycean" worlds.

I guess 'hydrogen' + 'ocean' = 'hycean'. There might be other explanations in Madhusudhan but I'm not reading the entire 25 pages to find them.

The capitalization, used by both sources, is puzzling: is it named after a person or place? A sci-fi author, perhaps? Otherwise, it should be lowercase. Also, anyone inventing a word should be required to grace us with a pronunciation.

What is the point of peer review if they don't catch these issues? ;)

[0] https://iopscience.iop.org/article/10.3847/1538-4357/abfd9c

Unsure why it's capitalized in the article (it shouldn't be, consider terms like ice giant and sub-Jupiter or even the hycean planet Wikipedia page) but I'll point out that there's a pun there you've missed. High seas.