$Assumptions={n>0,d>1,m>0,h>0,Σ>0,t>0,β>0,γ>0,ν>0,ℳ>0,H>0,𝒮>0,α>0,δ>0,X>0};

f=Σ (n^((d-1)/d))-h m n;

sol=Solve[D[f,n]==0,n]

ff=f/.sol[[1]]//FullSimplify

ff=H m(((H m))^(-d))Σ(((Σ))^(d-1))

ff=ff/.{m->(t^β)ℳ,Σ->(t^μ)𝒮}/.μ->{-ν+γ+2β}//FullSimplify

FullSimplify[ff//.{ν->(2-α)/d,γ->2-α-2β,δ->(2-α)/β-1,H->X (t^(β δ))}]

Plot[Exp[-1/x],{x,0,1},PlotStyle->{Thick,Black},Frame->True,LabelStyle->{FontFamily->"CMS Concrete",Black}]

Plot[ Exp[-1/x],{x,0,1},PlotStyle->{Thick,Black},Frame->True,LabelStyle->{FontFamily->"CMS Concrete",Black}]

sol=Solve[D[t (x^2)+u (x^4)-h x,x]==0,x];

Plot[Evaluate[Flatten[{Re@#}&@x/.sol/.{u->1,t->Cos[θ],h->Sin[θ]}]],{θ,0,2π},Axes->False]

Plot[Evaluate[Flatten[{Arg@#}&@t (x^2)+u (x^4)-h x/.sol/.{u->1,t->Cos[θ],h->Sin[θ]}]],{θ,0,2π},Axes->False]

Plot[Evaluate[Flatten[{#}&@D[t (x^2)+u (x^4)-h x,{x,2}]/.sol/.{u->1,t->Cos[θ],h->Sin[θ]}]],{θ,0,2π}]