The heading “Why are some apps so large on my display?” says Omarchy assumes a 2x high-resolution display, which sets GDK_SCALE to 2 in ~/.config/hypr/monitors.lua. On a 1x display, change local omarchy_gdk_scale = 2 to 1, then restart any app that is still oversized. The chapter points to the monitors page for the rest.
Manual heading: Why are some apps so large on my display?
Set the GDK scale to 1 on a 1x display
The manual says Omarchy assumes a 2x display and tells 1x displays to change omarchy_gdk_scale from 2 to 1 in monitors.lua.