  The quest to manipulate and understand superconductivity demands exploring
diverse materials and unconventional behaviors. Here, we investigate the BKT
transition in synthesized ReN$_x$ thin films, demonstrating their emergence as
a compelling platform for studying this pivotal phenomenon. By systematically
varying synthesis parameters, we achieve ReN$_x$ films exhibiting a BKT
transition comparable or even surpassing the archetypal NbN$_x$ system.
Detailed current-voltage measurements unlock the intrinsic parameters of the
BKT transition, revealing the critical role of suppressed superconducting
volume in pushing ReN$_x$ towards the two-dimensional limit. Utilizing this
two-dimensional electron system, we employ Beasley-Mooij-Orlando (BMO) theory
to extract the vortex unbinding transition temperature and superelectron
density at the critical point. Further confirmation of the BKT transition is
obtained through temperature-dependent resistivity, current-voltage, and
magnetoresistance measurements. Our findings suggest that native disorder and
inhomogeneity within ReN$_x$ thin films act to suppress long-range coherence,
ultimately driving the system towards the BKT regime. This work establishes
ReN$_x$ as a promising material for exploring BKT physics and paves the way for
tailoring its properties for potential applications in superconducting devices.
