EatReminder

The mod watches the hunger bar on each client tick and checks whether the item in the main or off hand carries the minecraft:food data component, so vanilla and modded food both count. When hunger falls six points or more below full with no food held, it fires a single alert. A short pickup sound plays once, and a message appears above the hotbar.

A badge in the upper-left corner of the HUD shows Eat N, switching to red when hunger falls to two points under the warning level. The message and sound fire again only if hunger keeps dropping, so a starving player is not spammed. The badge disappears the moment hunger recovers or food goes into either hand, and the reminder goes quiet as soon as something edible is picked up.

The reminder can be switched on or off with the H key. The mod is client-side only, so servers run without it and players install it alone. It needs Fabric API and is released under the MIT License; the mod is not open source. Files exist for 1.21.8, 1.21.9, 1.21.10 and 1.21.11, with 1.0.0 for 1.21.11 as the latest file.