I doubt that’s true. At minimum it’s going to hit an enormous quantity of micrometer sized objects.

It’s gravitationally bound to the Milky way so it’s going to keep wandering into and out of star systems for a very long time. We’re talking a large multiple of the age of the universe meanwhile plenty of space rocks show encounters with other space rocks on a vastly smaller timescale. If nothing else it’s got decent odds of being part of the star formation process. Stars are ~10% of the milky way’s mass and star formation is going to continue for a while.

Supposing that it does become part of a new star, and some "nearby" civilization had sufficiently precise instruments...would that be a detectable anomaly? Like some atoms of Plutonium still haven't decayed, and isn't that weird that Plutonium's spectral signature is present in this new star? Or is that just something that happens because some plutonium is created in a supernova and might just have been floating around anyway.

Quite. It will hit the occasional something, eventually. If nothing else it will be mildly bathed in radiation of some sort.

It's going to hit gas that will slowly but inexorably sputter it to nothing.