The Litematica overlay experiences z-fighting with existing blocks. I don't see an issue pointing this out in the litematica issues, so I'm pretty sure it is only with canvas. (Haven't had time to test vanilla yet)

i have renderBlocksAsTranslucent enabled and don't have as much of an issue as far as i can see, but i still have a bit of z-fighting on things like chests on glass

Does the problem go away if you turn off Batched Chunk Render in the Canvas config menu?

I'm guessing this may be the same root cause as #132

There is still z-fighting on the blocks on the ground, though the ones on the wall and ceiling are fixed.
Also I think turning it off is a bit bugged...

Nevermind, the chunks wouldn't load unless I disconnect then rejoin.