What nondairy milk does not curdle when heated?
Assuming the curdling happens when added to the coffee:

Hot soymilk is even more sensitive to curdling from acids than dairy milk. UHT (soymilk, not dairy) varieties are generally considered less prone to that effect, trying these might be worth it.

Oatmilk is often considered the best nondairy alternative for this scenario.

If palatable, this trick could also help:

Why does salt prevent soy milk from curdling in hot coffee?