3 years later, how strong is the evidence for planet 9? I came across post in quora where somebody said that "most astronomers no longer think Planet 9 exists" and being somewhat shocked by that, I did a google search and found a fairly recent article that claims exactly that.

It can take several years to prove a negative within pretty good certainty, as opposed to a discovery which can be checked pretty quickly.   Because I don't want to wait several years, I wanted to ask if the general consensus is that Planet 9 probably doesn't exist?  Or is there still a respectable amount of belief among astronomers in the original evidence and any new evidence that's followed?

If it ends up not existing, I'll be sorry to hear it.   It was a fun story when it lasted.
It's worth noting that Siegel's article seems to extrapolate from one paper (Shankman et al., 2017) to "most scientists" without much justification, so it's not particularly clear what most scientists think anyway (and that's before we get into the question of whether the "most scientists" referred to includes scientists whose discipline is not astronomy-related). Usually in these kind of situations there's a lot of back-and-forth as new objects are found in the outer solar system and the analyses of systematic errors and biases in the various surveys are refined. If there is an actual detection of Planet&nbsp;9, that would resolve things fairly definitively, the reverse situation is going to be rather more difficult to prove.

In response to the OSSOS paper (Shankman et al., 2017) Michael Brown and Konstantin Batygin released a new analysis of the clustering in the outer solar system, taking into account the OSSOS results that are the subject of Ethan Siegel's article. The paper can be downloaded from the arXiv. Brown also has a Twitter thread summarising the result. From the paper, their conclusion on the apparent absence of clustering in OSSOS:


  That is,
  the uncertainties in the measurement of clustering from
  the OSSOS data are so large that OSSOS would not be
  capable of confidently detecting the clustering seen in
  the larger data set even if it were real and present in the
  OSSOS data. Because of the limited survey region and
  small number of detected objects, OSSOS observations
  are equally consistent with being drawn from a uniform
  distribution of longitudes of perihelion and with being
  clustered in longitude of perihelion as strongly as seen
  in the ensemble data. No conclusions on clustering of
  longitude of perihelion observed in the complete dataset
  can be drawn from the OSSOS data.


They do note that this does not necessarily prove the existence of Planet&nbsp;9, but in the absence of Planet&nbsp;9 there would still need to be an explanation for the clustering.

Batygin et al. subsequently posted a review of the Planet Nine hypothesis on the arXiv, favouring a lower planetary mass and a less eccentric orbit than originally proposed. The new parameters do not favour Planet&nbsp;9 as an explanation for the solar obliquity.

On the anti-Planet&nbsp;9 side of things, it's worth looking into Kavelaars et al. 2019, a subsequent paper from the same authors as the study based on the OSSOS data, who note that there seems to be an absence of objects with perihelia ($q$) between 50 and 75&nbsp;AU that would be expected if a planet was causing the alignment, which so far doesn't seem to be explainable by detection bias.


  A survey
  that might have detected a TNO at $a ∼ 500\ \mathrm{au}$
  and $q ∼ 75\ \mathrm{au}$ is actually more likely to have detected objects with similar $a$ but smaller values
  of $q$. The same is true of the other $q &gt; 75\mathrm{au}$
  detections: the lower-$q$ but similar $a$ detections
  are always more likely. Thus, the lack of detections in the $50 &lt; q &lt; 75\ \mathrm{au}$ range may be indicating that there really is an absence of TNOs
  on orbits in this range. This strongly contradicts models of orbital evolution that include
  an additional planet, as the gravitational action of such an object would cause TNOs to
  be distributed across a range of $q$ values at any
  given moment (Figure 2; Shankman et al. 2017a;
  Lawler et al. 2017). Thus, if the lack of objects
  in the $50\ \mathrm{au} &lt; q &lt; 70\ \mathrm{au}$ range is real, the
  hypothesized external planet can be excluded.


It still is an active area of research, so it remains to be seen how the various studies will hold up.