In this case: can we build self-replicating machines? Yes. Is there any specific reason to think that the great filter might lie between now and deployment of the machines? No, because we've already had the capability for 35+ years, just not the political will or economic need. We could have made it already in an alternate history. So since we know the outcome (the universe permits self-replicating space-faring machines, and we have had the capability to build them for sufficient time), we can update based on that evidence now. Actually building the machines therefore provides zero new evideence.

In general: anthropic reasoning involves assuming that we are randomly selected from the space of all possible universes, according to some typically unspecified prior probability. If you change the state of the universe, that changed state is not a random selection against a universal prior. It's no longer anthropic reasoning.