Of course, we cannot know how much truth is in this claim, because nowadays it is fashionable for companies to emit such claims.
The fact that it processes 300 mm silicon wafers makes it unlikely that it also makes SiC or GaN devices, which would require separate production lines.
I believe that it is much more likely that here are made only the silicon ICs used as controllers for SiC and GaN power devices that are made in other factories.
They could also make low-voltage power MOSFETs in this new fab. IGBTs are being replaced more and more frequently by silicon carbide devices, so I doubt that Infineon would need a production expansion for IGBTs. Moreover, IGBTs are made on a different kind of wafers, and I do not know whether those are also available as 300 mm wafers.
For a company that has a great number of factories it would not make sense to build a combined Si/GaN/SiC factory, instead of building separate factories for each semiconductor material, because they are made on substrates that are incompatible mechanically, so they must use separate installations anyway.
They also use different chemicals for various process steps and keeping them in separate factories simplifies the avoidance of cross-contamination between the production lines.