Translucent items are invisible when held.

[Moonyol]

Items that are translucent are invisible in 1st person when held, these include stained glass, stained glass panes, tinted glass, and ice.

moreculling-1.20.4-0.24.0.jar fabric-api-0.97.1+1.20.4.jar cloth-config-13.0.121-fabric.jar fabric-loader-0.15.11-1.20.4

[CommandGenius]

This is fixed in 1.21, though very sloppily.