Could the planet have been captured after the ballooned red dwarf shrank? E.g. a wandering planet. Or could something have made its orbit shift, e.g. if it was farther out and now it’s closer in?

Planet 8 Ursae Minoris b orbits a star some 530 light-years away that is in its death throes. A swollen red giant, the star would have been expected to expand beyond the planet’s orbit before receding to its present (still giant) size. In other words, the star would have engulfed and ripped apart any planets orbiting closely around it. Yet the planet remains in a stable, nearly circular orbit.