\[ -a x y(x)-b+y^{(5)}(x)=0 \] ✗ Mathematica : cpu = 0.169622 (sec), leaf count = 0 , DifferentialRoot result
\[\left \{\left \{y(x)\to \text {DifferentialRoot}\left (\{\unicode {f818},\unicode {f817}\}\unicode {f4a1}\left \{-b-\unicode {f817} a \unicode {f818}(\unicode {f817})+\unicode {f818}^{(5)}(\unicode {f817})=0,\unicode {f818}(0)=c_1,\unicode {f818}'(0)=c_2,\unicode {f818}''(0)=c_3,\unicode {f818}^{(3)}(0)=c_4,\unicode {f818}^{(4)}(0)=c_5\right \}\right )(x)\right \}\right \}\]
✗ Maple : cpu = 0. (sec), leaf count = 0 , could not solve
dsolve(diff(diff(diff(diff(diff(y(x),x),x),x),x),x)-a*x*y(x)-b=0,y(x))