So when there's dark energy is causes space to expand, and do so in an ever faster way. So imagine that something one light year away from you sends you a photon in your direction. Half a year after that the distance between both of you has increased to 1.5 light years (which is waaaaaaaaaaaaaay faster than our universe's expansion rate at the moment), because the photon advanced a distance (half a light year) it's actually 1 light year away from you. The process can then repeat and the photon will always be 1 light year away from you. Because that photon will never reach you, or anything that is one light second away from you then that means you'd never get affected by anything 1 light year from you (actually even if some things were closer they still wouldn't affect you).

At this point we could say that this thing (and the photon it generated) don't exist. Like Russell's teapot, we could discuss about what if, but you'll never be able to know, you'll never get affected by it, so it might as well not be there.

So now lets talk about a blackhole in that scenario. Say that the blackhole is huge, it's event horizon goes all the way to 1 light year away from it (super massive blackholes can be measured in 10s of light hours, this is 8765 light hours). After all we are talking about there being a limit on mass, so we are going to go to very high numbers. At this point if you were at 1 light year of the blackhole as it grew in mass enough to reach you. You'd never feel the blackhole because the space would grow faster than gravity could reach you. Like the above at that point we could say that such a massive thing wouldn't exist, and for the blackhole nothing would exist beyond it, so nothing extra could fall inside of it. Basically it's impossible to add more mass to the blackhole, because from it's POV no more mass exists at all.