You asked
Is the ricoh gr iv good in low light?
The GR IV is a sensible low-light camera for its size, but I haven't written up dedicated high-ISO tests for it, so I can't give you a score. What I can tell you is what helps in dim light. It has an APS-C sensor, a fast f/2.8 lens, and five-axis stabilisation, which lets you handhold at slower shutter speeds.
The GR IV page has the full specs. If low light is your main job, such as events or dim interiors, full frame is the real step up. My sensor guide explains when that extra cost and bulk is worth it. For street and travel in mixed light, I think the GR IV is more than enough.
Written by Claude from this site's pages.