What it fixes

GTFO's menu font has no CJK glyphs, so TextMeshPro draws them with a fallback font, in a separate "submesh" object with its own renderer. The game only ever sets up a text's own renderer, so that part of a text is not properly handled:

• is not clipped by scroll windows: it spills over the window's edge;
• can end up behind a popup's background: inside the popup it is invisible, and only shows where it sticks out.

This affects any text with fallback-font glyphs in a scrolling list or popup: the game's own menus in CJK (mixed w/ Latin charset especially).

How

Every submesh inside a clipped window is tracked together with its text, and once per frame it is given its text's sorting layer and clipping data.