You are confusing reported and estimated casualties. The reported civilian deaths in the nine-month Battle of Mosul were around 10k. A later estimate put the total number of civilian deaths to ~40k.

The numbers from Gaza are reported deaths, and nobody is seriously disputing them anymore. They are pretty consistent with the claims Israel is making. About two thirds of them should be civilians. That means a bit over 10k dead civilians after 2 months. True civilian casualties are likely higher, but the situation on the ground makes reliable estimates impossible.