Companion Mod

If you don't want to have crouch as your vein miner key, then you can install this mod which is paired with the plugin

https://www.curseforge.com/minecraft/mc-mods/veinminer-companion

Enabling the Mod

Install the mod with fabric and join the server.

Once in the server run: /vm mode client

Configuring the Mod

The mod allows you to configure what keybind you want to use

Disabling the Mod

To disable the mod join the server and run: /vm mode sneak