Firstly do you need two IFs, if the first condition doesn't hold then the second must so you can use just

=IF(M4>H4,"No","Yes")

adding ISERROR would then give you

=IF(ISERROR(IF(M4>H4,"No","Yes")),"",IF(M4>H4,"No","Yes"))

but as M4 and H4 must contain errors for that formula to give you an error you could probably shorten like

=IF(ISERROR(M4&H4),"",IF(M4>H4,"No","Yes"))