There are speculations that most of Shakespeare's love sonnets were written about men, do these speculations have some truth to it

It is not really an issue of speculation that Shakespeare's first 126 sonnets were addressed to an unknown young man. This is the accepted scholarly view, and his sonnets are divided into the "Fair Youth" sonnets and the "Dark Lady" sonnets.
It is clear from the content of the sonnets themselves that a man is being addressed. In several, the speaker is encouraging the subject to reproduce "the treasure of thy lusty days" (Sonnet 2) by producing an heir—"die single and thine image dies with thee" (Sonnet 3). The speaker is concerned that the subject's "unused beauty must be tombed with thee" (Sonnet 4) if it is not reproduced in the form of a child. Shakespeare also makes liberal use of puns on words like "will" and "prick'd," which are, of course, penis jokes. Look at Sonnet 20, in which the speaker praises the "woman's face" of his subject, "the master mistress of my passion," who is "a man in hue." In this sonnet, the speaker seems to express, fairly straightforwardly, enormous admiration for the subject's beauty, but notes that nature "prick'd thee out for women's pleasure," in "adding one thing to my purpose nothing"—meaning that it's a shame such a beautiful creature should have been adorned with one extra thing (a penis) which makes him useless for the speaker's "purpose," that is, sexually.
If you read all the sonnets from beginning to end, it's clear that they are connected. While some of the "love sonnets" ("Let me not to the marriage of true minds / Admit impediments," for example) may not include any specific features which mark them out as being about either a man or a woman, the overarching sonnet cycle makes it evident that sonnets 1–126 are all addressed to the same subject. There is enormous unity of theme and sentiment, which is why it is accepted that these sonnets all concern the same Fair Youth.
This is not to say, however, that there is no speculation at all about the sonnets. They are sonnets addressed to a man, and some of them are love sonnets, but that is not to say that Shakespeare is dealing with a sexual love. Some argue that Shakespeare, in writing 126 poems praising the beauty of a young man, must have been what would now be called bisexual, but it isn't sensible to apply modern labels to a historical context. Shakespeare's poems may be romantic without being sexual; some, like the one I discussed earlier, even seem to suggest that the poet had some sexual interest in the young man but would never have pursued it because he was meant "for women's pleasure." There has also been a lot of speculation as to the possible identity of the young man and whether or not he is the "Mr W.H." mentioned in the preface to the first edition of the sonnets, with many candidates being identified based on "clues" in the sonnets suggesting, for example, that the young man was of a higher social class than the poet. Ultimately, however, we will never know who the young man was.