Bostrom's logic is so laughably bad, but it's worth refuting clearly.

To tackle point (1), note that Bostrom assumes a Doomsday argument [0] and that there are both pre-human and post-human modes of life which are qualitatively different from ours. But it assumes that the structure of the Universe is relatively constant, and that is not the case. For example, we live in a time when galaxies are clearly visible in the night sky; were we to have been born much sooner or later, we wouldn't know about galaxies, and we might further be fooled into thinking that the Milky Way is unique or special.

Point (3) is really the one that Bostrom wants for us to conclude as true, but it's completely inaccessible and unfalsifiable. Just like Christopher Columbus could never sail to the Garden of Earthly Delights, it's not possible for us to falsify the proposition that we live in a simulation, whether it be a Spinozan world, a Great Programmer world, or whatever quasireligious interpretation one might want to use.

We can now freely embrace (2). We run plenty of simulations of pre-human life. One might object that we do not model all of the details of the inner experiences of such life, but of course there is no evidence for such inner experiences and we can ignore them entirely [2].

There's other critiques of this argument. They usually boil down to some sort of post-selection [1]: Bostrom first post-selects to insist that there will inevitably civilizations which could plausibly simulate us, and then uses the post-selection to lock us into already being simulated.

And, of course, there's a final argument from the outside: This would have all been just as true in the 1600s as it would be today, were the argument to be rock-solid. But then, computers would not have existed in the societies of the 1600s, so the argument would have to be prefaced by an introduction which doesn't just wax poetic about how tiny future computers would be, but also explains computation, quantum mechanics, black holes, etc. However, in the 1600s, Spinoza [3] was able to put forth the argument that we are all simulated by the mind of God, and his deductions and rules were not much different from Bostrom's. Spinoza and Bostrom seem to have the same conceptualization of the Universe, and are following the arguments that they think will lead them there best. But those arguments are hopelessly and obviously covered in the technology and ideas of the time. Therefore, if there is a way in which we are simulated, then the actual argument which proves it will have to come with a massive introduction which justifies it, not just by using our current words and ideas, but by introducing some sort of 25th-century mathematics and physics.

Oh, but wait, why would simulations become possible arbitrarily in the 25th century? We can iterate, and imagine that the hypothetical civilization which simulates us is indefinitely far in the future. When we predict this far into the future, not only do our models break down, but our ability to model breaks down. Bostrom far overshoots with this argument!

[0] https://en.wikipedia.org/wiki/Doomsday_argument

[1] https://en.wikipedia.org/wiki/Postselection

[2] https://en.wikipedia.org/wiki/Philosophical_zombie

[3] https://en.wikipedia.org/wiki/Baruch_Spinoza