Standard candles (all these measurements of redshift according to distance, need us to actually get the distance of what we are measuring right) are the gift that keeps on giving.

This study (and many others, depending on the cosmic scales they use) mainly use Supernovas of Type Ia. I.e. the energy emitted by the supernova of a binary acreccion star, which is a star that is capturing the mass from another start that is very nearby and increasing its mass until it collapses into itself, increases temperature up to the point it starts fusing helium, and goes supernova with all the added energy.

That was (and still is now, with some corrections we found since middle last century) supposed to be the same everywhere. Problem is, we keep finding new corrections to it - like this study claims.

That is in fact the big claim of this study (ignore the universe expansion part), that they found a new correction to the Supernova of type Ia luminosity. It's a very big claim and extremely interesting if confirmed. But, like all big claims, it needs a big confirmation. I'm a bit skeptic TBH.