The standard model for blackhole formation predicts an upper bound on the mass of blackhole depending also on environment since the available amount of matter in environment is bounded. In the case of Milky Way the bound is about 20 solar masses. Now however a blackhole like entity (BHE) with mass about 70 solar masses has been discovered (see this) . I am grateful for Wes Johnson for the link. Also the masses of BHEs producing the gravitational radiation in their fusion have been also unexpectedly high, which suggests that standard view about BHEs is not quite correct.
In TGD framework the blackhole-like entities (BHEs) are volume filling flux tubes: the thickness of the flux tube is roughly proton Compton length. Also asymptotic states of stars are BHEs in this sense: the flux tube radius is some longer p-adic length scale coming in half octaves. The model leads to a correct lower bound for the radius and mass satisfied by neutron stars and standard blackholes. Also the masses of very light stars can be understood.
Model in its recent form does not give upper bound for the mass. For time reversed BHEs - analogs of white holes (WHEs) possibly identifiable as quasars - the mass of WHE comes from a tangling long cosmic string and there is no obvious upper bound. Even galactic BHEs would correspond to WHEs made quantum jump to BHEs at the level of magnetic body: in this state the flux tube forming counter the magnetic field is fed back from environment. A breathing spaghetti.
In standard model the mechanism for the formation of blackhole is different since there is no flux tube giving the dominant dark energy/dark matter contribution. Therefore the upper bound for mass - if there exists such - is expected to increase. An upper bound could come from the transformation of de-entangling of flux tube so that spaghetti would straighten.
The simplest model predicts that only the flux tube mass contributes. The mass of the ordinary matter going to BHE would transform back to dark energy/mass of the flux tube. The process would be time reversal of the process making sense in zero energy ontology (see this and this) in which the magnetic energy of flux tube transforms to ordinary matter: time reversal for the TGD counterpart of inflation.
See the chapter Cosmic string model for the formation of galaxies and stars of "Physics in many-sheeted space-time" or the article with the same title.