(my questions in connection to this paper have something to do with the cosmological principles of homogeneity and isotropy that as far as i understand these work well in terms of what we acutally observe in the universe like CMBR, WMAP and also when it comes to BHs, what happens to Birkhoff's theorem? according to this paper, BH mass increases as affected by cosmological expansion in turn, the increase in BH mass would contribute an effective cosmological constant to accelerate the expansion so that the universe in effect speeds up more and more in its expansion)
to quote from the authors of the paper
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The redshift dependence of the mass growth implies that, at z less than/aprrox 7, black holes contribute an effectively constant cosmological energy density to
Friedmann’s equations.
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https://iopscience.iop.org/article/10.3847/2041-8213/acb704
i don't believe that BHs masses should change due to the expansion of the universe and the backreaction that as BHs change their masses in effect, they contribute to dark energy that speeds up the expansion i DO NOT believe it works that way. the best explanation there is to the late time accelerated expansion of the universe is the cosmological constant, other adhoc theories that don't depend on Bh's mass evolution