Fabric 1.21.1 1.1.6-patch2-fabric-alpha.1

Official Changelog

For Minecraft 1.21.1 / Fabric.

⚠️ This is an unstable Alpha build. Back up your worlds before playing, and do not keep important worlds in only one copy.

First public Minecraft 1.21.1 Fabric Alpha, including the oversized batch-task safeguards from 1.1.6-patch2 and the current 1.21.1 mainline feature set.
Fixed vanilla right-click interaction, and potentially left/middle mouse actions, becoming unavailable after leaving RTS mode.
Disconnecting, leaving a world, or reconnecting now force-releases RTS client input state so a stale session cannot keep intercepting vanilla controls.
The first in-world notice explicitly identifies the Fabric Alpha as unstable, asks players to back up their worlds, and shows the complete Alpha version string.

The full build and automated test suite passed.
Client startup was tested in a development environment containing Sodium, Lithium, C2ME, ModernFix, FerriteCore, ImmediatelyFast, EntityCulling, MoreCulling, Noisium, and Krypton.
All 46 GameTests passed with the optimization suite loaded, including the range-culling persistence boundary regression test.
This is a new Fabric port and real modpack compatibility still needs community testing. If something goes wrong, leave the world, restore from a backup, and include the log in your report.