I tried exporting this
RegionPlot[x^2 + y^3 < 2, {x, -2, 2}, {y, -2, 2},
Epilog ->
Text[Style["Lyman-\[Alpha]", 14, RGBColor[0.65, 0., 0.],
FontFamily -> "Latin Modern Roman"]]]
to pdf with Mathematica 13.3 on a Macintosh, and the exported picture looks fine.
