FormattedString is your best friend here, as you can add a glyph name to the string and get the glyph with the appendGlyph method.
so for your code:
newPage('A4Landscape')
font('SFMono-Regular')
fontSize(60)
txt = listFontGlyphNames()
t = FormattedString()
t.appendGlyph(txt[60])
text(t, (30, 30))
