This theory of antipodal focusing is disproved according to the intro to the cited source. The source says that the Chicxulub crater is offset from the antipodes by 130°. It also says that the impactor didn't have enough energy to cause melting at the antipodes. The cite says this disproves the antipodal theory.
Instead the new idea presented in the cite is that the impact generated a magnitude 9 earthquake worldwide and this caused volcanism to increase everywhere, through a now well established process by which nearby earthquakes can trigger increased volcanism. The Deccan traps started well before the impact, due to a rising "plume head", rising through the mantle which hapens every 20-30 million years, but after the impact they sped up and the chemistry changed.
Cite says:
The possibility that an impact at Cretaceous-Paleogene time caused Deccan volcanism has been investigated since the discovery of the iridium anomaly at Cretaceous-Paleogene boundary, with an emphasis on antipodal focusing of seismic energy. However, the Deccan continental flood basalts were not antipodal to the 66 Ma Chicxulub crater at the time of the impact, but instead separated by an epicentral distance of ~130°. Also, a Chicxulub-size impact does not in any case appear capable of generating a large mantle melting event. Thus, impact-induced partial melting could not have caused the initi-ation of Deccan volcanism, consistent with the occurrence of Deccan volcanism well before Cretaceous-Paleogene/Chicxulub time.
Instead, Deccan volcanism is widely thought to represent the initial outburst of a new mantle plume “head” at the beginning of the Réunion hotspot track
Accompanying press release from Berkely university says:
Michael Manga, a professor in the same department, has shown over the past decade that large earthquakes – equivalent to Japan’s 9.0 Tohoku quake in 2011 – can trigger nearby volcanic eruptions. Richards calculates that the asteroid that created the Chicxulub crater might have generated the equivalent of a magnitude 9 or larger earthquake everywhere on Earth, sufficient to ignite the Deccan flood basalts and perhaps eruptions many places around the globe, including at mid-ocean ridges.
“It’s inconceivable that the impact could have melted a whole lot of rock away from the impact site itself, but if you had a system that already had magma and you gave it a little extra kick, it could produce a big eruption,” Manga said.
Similarly, Deccan lava from before the impact is chemically different from that after the impact, indicating a faster rise to the surface after the impact, while the pattern of dikes from which the supercharged lava flowed – “like cracks in a soufflé,” Renne said – are more randomly oriented post-impact.
“There is a profound break in the style of eruptions and the volume and composition of the eruptions,” said Renne. “The whole question is, ‘Is that discontinuity synchronous with the impact?’”
Another cite here, "The Conversation" which is written by academics and is WP:RS.
More bad news for dinosaurs: Chicxulub meteorite impact triggered global volcanic eruptions on the ocean floor (2018)
Our observations suggest the following sequence of events at the end of the Cretaceous period. Just over 66 million years ago, the Deccan Traps start erupting – likely initiated by a plume of hot rock rising from the Earth’s core, similar in some ways to what’s happening beneath Hawaii or Yellowstone today, that impinged on the side of India’s tectonic plate. The mid-ocean ridges and dinosaurs continue their normal activity.
About 250,000 years later, Chicxulub hits off the coast of what will become Mexico. The impact causes a massive disruption to the Earth’s climate, injecting particles into the atmosphere that will eventually settle into a layer of clay found across the planet. In the aftermath of impact, volcanic activity accelerates for perhaps tens to hundreds of thousands of years. The mid-ocean ridges erupt large volumes of magma, while the Deccan Traps eruptions flood lava across much of the Indian subcontinent.