Sheldon is a white male who is desexualized.
Leonard is a white male who is desexualized.
Harold is a white male who is oversexualized in creepy ways.
And I'm not even sure "desexualized" is the right word. With both Raj and Leonard, at least, I remember there were many plot points about their difficulty with women. "Desexualized" to me would mean that they weren't even seen as people who are interested in sex or relationships -- that is, their status as having sexuality at all was minimized and never touched upon -- which was clearly not the case for either of them.
In any case, "relying on a stereotype" does not make something racist. When I watched the show (admittedly not for long; I probably got tired of it after a season or two), yes, there were certainly jokes that only worked because Raj was Indian, or Harold was Jewish, or Sheldon was neuro-atypical, but for the most part it was the stereotype "nerdy people are awkward in all sorts of social situations, especially when nerdy heterosexual men interact with women". Being Indian, or Jewish, or probably-autistic were secondary characteristics that gave them more color as people.
Sheldon could be more accurately diagnosed as "a total pain in the arse".
Raj embraces the role-playing sex game with scientist woman. The scene fades out implying they have a night of sex and wine.
Where exactly is your "desexualisation"?
Aren't all the male characters in the show this way?
Is the show doing "Character who is Indian male lacks confidence with women" ?
Or is it doing "Character lacks confidence with women because he's an Indian male"?
There's a world of difference.