RectPick lets you select items in a rectangular area of an inventory and transfer them to another inventory.

Here is a demo.

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Requirements
NeoForge 1.21.1

Installation

1. Install NeoForge 1.21.1
2. Put the mod jar file into mod folder.

Configuration
By default select/transfer key is C but you can configure via key bindings.

Source Code
https://github.com/Pepton-0/RectPick