There have been multiple credible debunks as of late, exx.:

* Sabine Hossenfelder: https://www.youtube.com/watch?v=RjzL9cS3VW8 update: https://www.youtube.com/watch?v=LoKWourNJEs&t=875s

* Sixty Symbols: Bad Science and Room Temperature Superconductors https://www.youtube.com/watch?v=zl-AgmoZ5mo

* Thunderf00t: LK-99 BUSTED!!! https://www.youtube.com/watch?v=p3hubvTsf3Y

Especially the last two are utterly scathing, with Prof Moriarty in the Sixty Symbols video pointing out that the one measurement curve they show—shows nothing WRT superconductivity (because the scaling is wrong). Also, he says that the entire measurement has been done in a sloppy way, with way too few data points. Lastly, neither the sensationalist title of the paper nor its equally grandiose concluding remark instill trust.

Thunderf00t (aka Philip Mason) destroys the video of Two bit da Vinci about LK-99 for every. single. claim. the guy makes, and especially pointing out that the GAME changing!! Revolutionary!!! effects of having room-temperature superconductors are not that; you can read up on Wikipedia where they'll tell you that the 'high-temperature' (i.e. liquid nitrogen as opposed to liquid helium) superconductors have been looking for applications for decades, with little to show. Cooling is only part of the problem, both technically and cost-wise; one problem is that electric motors with superconductive coils suffer from instability problems, and superconductivity will abruptly end when there is too much current (to my understanding).

Both Moriarty and Mason demonstrate the diamagnetic hover effect with a thin plate of graphite, which is one of the possible causes for the hovering chunk of material seen in the LK-99 video; Moriarty rightly points out that with one end of that chunk in the air and one down on the magnet, it actually looks like this is a tiny magnet with the poles on the far ends of the materials. Neither ferromagnetic nor diamagnetic materials are new by any stretch; I imagine if you had a very strong diamagnetic material, that could be interesting for some moving parts in machines, but it won't change anything fundamental.

I've since come to the conclusions that the authors of the paper are completely delusional or frauds. They have apparently been working on this for 25 years (the 99 in LK-99 stands for year 1999); if they were out to conceive people one would think they would not have spent 25 years in a laboratory before coming out.

For a number of reasons LK-99 reminds me of the EM drive, for which I recommend to watch another of Thunderf00t's videos, EM Drive BUSTED!, https://www.youtube.com/watch?v=jCAqDA8IfR4 . It's entertaining but also a little sad to see the inventor talk about it (right after the start of the video) as though the effect was real and will give us flying cars, fast transportation on Earth and to Mars, solve global warming and whatnot. Coincidentally this guy also had his moment of rapture in 1999 (as in, LK-99) and been working on it for many, many years. Judging from the filmed interviews, he's not a liar, just someone with two weaknesses—he can't believe he's not right in his beliefs and opinions, and, second, he had an utterly wonky crackpot idea. Now he's captured in the false belief that an EM drive (i.e. a metallic cavity that has photons bouncing around inside, otherwise known as an MTIAWBDOAKONIFE (a 'machine that is and will be devoid of any kind of net impulse, for ever', save for minuscule effects of excess heat at one end) could move things, and at scale (the thrust of existing models has been shown to be ridiculously small, especially when compared to energy input).