>>1013105
There's also a native workaround for that. https://blender.stackexchange.com/questions/304119/is-it-possible-to-mirror-lattice-edits
I just made Chatgpt script it into an addon https://files.catbox.moe/qrkgfd.py

First parent your mesh(es) to a lattice, then select the lattice, right click in Object mode>Mirror lattice on X