Yes, at some point Boltzmann brains become higher likelihood but don't forget that interventions are not limited to prior history, e.g. someone builds a machine that performs whole-body surgery based on the timing of radioactive decay. Still more likely to end up with a functioning body than a Boltzmann brain. Most likely to end up with a weirder but more likely intervention (low expectation of it actually working, but not infinitesimal) (and from anthropic perspective)