Style["!(*SubscriptBox[(t), (2g)])  Element", FontFamily -> "TeX Gyre Pagella",  FontSize -> 22]

plot1=Plot[x^2, {x, 0, 3} , Frame -> True];
tex1 = Style["Element ", FontSize -> 22, FontFamily -> "TeX Gyre Pagella"];
tex2 = Style["!(*SubscriptBox[(e), (g)])    Element", FontSize -> 22, FontFamily -> "TeX Gyre Pagella"];
tex3 = Style["!(*SubscriptBox[(e), (g)])", FontSize -> 26, FontFamily -> "TeX Gyre Pagella"];
legend1 = GraphicsRow[{tex2}]
legend2 = GraphicsRow[{tex3, tex1}]


Legended[ Show[ plot1, ImageSize->850,PlotRange->{{0.1, 1.02},{-0.05,5.3}},
Epilog ->  {Directive[{Black, Dashing[0.02]}],Line[{{0.820,0},{0.820,6}}]},
Prolog-> Inset[Style[inset,Magnification>0.6], Scaled[{0.25,0.76}], Scaled[{0.5,0.5}], Scaled[{1,1}]]],
Placed[LineLegend[{Directive[Black, Magnification->3.5], Directive[Red, Magnification->3.5]}, {legend2,legend2}], Scaled[{0.58, 0.16}]]]