The virtual OBS camera never ever showed up in device manager. In device manager only devices powered by device drivers are showing up, while OBS doesn't come with a device driver but instead dynamically registers its virtual camera at runtime. This is probably a very lightweight method of bringing video into Windows and is specifically intended by Microsoft to be used by apps that provide virtual cameras, while writing a whole device driver is something rather complex and time consuming.
Most Windows apps support both kind of cameras. The Windows native camera app only supports cameras with a device driver and never showed the OBS camera, while every other regular Windows app I know also recognizes the dynamically registered OBS virtual camera.
So just use the OBS camera with your app and ignore the fact the Windows native camera doesn't support it. It's a not really an important issue, and it's also not a sign of something being not right.