We found infinitely many integer solutions to 
$$X^4+Y^4-18Z^4= -16 \qquad (1)$$.

The interesting part in this diophantine equation is the sum of
the reciprocals of the degrees is $3/4 < 1$, which is related to
[Vojta's more general abc conjecture][1].

>Q1 Is this result trivial or known?

Consider the diophantine equation
$$ aX^n+bY^m+cZ^l=d \qquad (2)$$

where $1/n+1/m+1/l < 1$. Solution of (2) is trivial if almost always
$d \in \{aX_0^n,bY_0^m,cZ_0^l\}$ and the sum of the other two
monomials vanishes.

>Q2 Is there (2) with infinitely many integer non-trivial solutions,
except for generalization of (1) with $n=m=l=4$?


  [1]: https://arxiv.org/abs/math/9806171