It's unclear which one is responsible for this.
As the title suggests, when activated in conjunction with the Nauvis Day mod,
The following error occurs.

146.616 Mods to disable:Failed to load mods: File not found: NauvisDay/graphics/terrain/stone-path/hr-stone-path-o.png

Mods to be disabled:
窶｢ NauvisDay (1.18.12)

I'm quite sure it's the other mod's fault

They need to change
NauvisDay/graphics/terrain/stone-path/hr-stone-path-o.png
to
__NauvisDay__/graphics/terrain/stone-path/hr-stone-path-o.png

for Factorio to find the file properly

I said "when activated in conjunction with".

Each of these mods can be activated individually.

this is now fixed

I confirmed.
Thank you for your appropriate reaction.

All I did was add a dependency to the other mod. I don't know why the issue was happening in the first place

NauvisDay does not even add stone path, nor does any graphic file by that name exist at all, nor does the string "path" exist in the entire mod: https://i.imgur.com/3zrkjZx.png