\[ y''(x)-h\left (y'(x),a x+b y(x)\right )=0 \] ✗ Mathematica : cpu = 0.122128 (sec), leaf count = 0 , could not solve
DSolve[-h[Derivative[1][y][x], a*x + b*y[x]] + Derivative[2][y][x] == 0, y[x], x]
✓ Maple : cpu = 0.151 (sec), leaf count = 115
\[ \left \{ y \left ( x \right ) ={\it ODESolStruc} \left ( -{\frac {a \left ( \int \!{\it \_b} \left ( {\it \_a} \right ) \,{\rm d}{\it \_a}+{\it \_C1} \right ) -b{\it \_a}}{b}},[ \left \{ {\frac {\rm d}{{\rm d}{\it \_a}}}{\it \_b} \left ( {\it \_a} \right ) =-h \left ( {\frac {-a{\it \_b} \left ( {\it \_a} \right ) +b}{{\it \_b} \left ( {\it \_a} \right ) b}},b{\it \_a} \right ) \left ( {\it \_b} \left ( {\it \_a} \right ) \right ) ^{3} \right \} , \left \{ {\it \_a}={\frac {ax+by \left ( x \right ) }{b}},{\it \_b} \left ( {\it \_a} \right ) ={\frac {b}{a+b{\frac {\rm d}{{\rm d}x}}y \left ( x \right ) }} \right \} , \left \{ x=\int \!{\it \_b} \left ( {\it \_a} \right ) \,{\rm d}{\it \_a}+{\it \_C1},y \left ( x \right ) =-{\frac {a \left ( \int \!{\it \_b} \left ( {\it \_a} \right ) \,{\rm d}{\it \_a}+{\it \_C1} \right ) -b{\it \_a}}{b}} \right \} ] \right ) \right \} \]