Question

Cirrus clouds form in what layer

Answer 1

I believe Cirrus clouds are part of the genera high-etage and will form from 5,000 m in the troposphere.

Answer 2

High clouds include cirrus, cirrocumulus, and cirrostratus clouds. These clouds are made up of either ice or water droplets, but they are usually made up of ice crystals. Water clouds tend to have sharp edges, and ice clouds are more wispy.

Not sure if this helps, but check this link.

https://www.windows2universe.org/earth/Atmosphere/clouds/cloud_heights.html