See each camera's uptime on Device health
On Device health › Cameras, an Uptime · 30d column shows the percentage over a bar: green from 99%, amber from 95% and red below that. Hover to see hours down. With under a day of data it shows a dash, not 0.
The Site Device Health Report PDF shows camera uptime too, as a summary figure, for each site and for listed cameras.
Uptime is the share of hours when a camera wasn't unhealthy. Hours where its health is unknown or suppressed don't count.