QuadHotbar
QuadHotbar adds up to four switchable hotbars for NeoForge 1.21.1 and Forge 1.20.1.
It is a convenient Multi-Hotbar port created for comfortable building and working with many items. The project was made with support from KharkivTiles 1:1.

Status
This is a pre-release. QuadHotbar is intended to reproduce much of the feel and functionality of Multi-Hotbar for Minecraft 1.12.2, while adapting it for modern NeoForge.
Since the last alpha, the code has been significantly rewritten and refined. Core hotbar switching and rendering are working, but small compatibility and polish changes may still happen before the stable release.
For multiplayer, QuadHotbar must be installed on both the client and the server. If the server does not have Quad Hotbar installed, the extended hotbars will not work there.