Formatting legend text font

Try using Style in the option values for PlotLegend->{...}. For example:

  Plot[{Sin[x], Cos[x]}, {x, 0, 2 Pi}, 
  PlotLegend -> {Style["sine", Red, Bold, 18], "cosine"},  
  LegendLabel -> None]

gives:

enter image description here

In case you have multiple legends, just use an explicit pure function:

PlotLegend -> Style[#, Red, Bold, 18] & /@ {"apple", "pear", "grape"}

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