The sonnet is, at least on the surface, as simple as can be: the speaker says that when they think about the past, they are sad, but when they think about “thee (dear friend)”, they are happy.
That’s pretty much all we can say about the subject of the poem in isolation. The details that we are given are completely generic—the speaker is sad because of the “lack of many a thing I sought”, “old woes”, “friends hid in death’s dateless [eternal] night”, and so on. There is nothing specific here: we all suffer from lacks and woes, and grieve at the death of friends and loved ones.
So if we want a more specific interpretation then we have to bring something from outside the text. For example, if we think that Shakespeare might have been writing in propria persona then we can try to identify the elements of the poem with corresponding elements in his biography. Unfortunately we are stymied here by the lack of biographic detail: we simply don’t know enough about Shakespeare’s life to reliably identify the “dear friend” of this sonnet.
With that as background, we can tackle the Linda Sue Grimes essay. Grimes claims that
The “dear friend” he is addressing in this sonnet is his talent, his ability to write sonnets.
Linda Sue Grimes (2021). ‘Shakespeare Sonnet 30: “When to the sessions of sweet silent thought”’. archive.org.
The only argument that Grimes makes for this claim is this:
The speaker’s reliance on his God-given talent remains a strong feature in this set of sonnets. He repeatedly demonstrates that he knows he is a great poet.
Here “this set of sonnets” refers to the “Muse Sonnets”, a label that Grimes applies to the sonnets conventionally known as the “Fair Youth Sonnets” (18–77 and 87–126):
Sonnet 30 belongs to that thematic group which is mistakenly thought to be addressed to a young man and which has been mislabeled “The Fair Youth Sonnets.” However, no young man appears in any of the sonnets in this group. No person at all appears in any of sonnets in this group. The speaker muses only on his poems and his ability to compose them; thus, “The Muse Sonnets” offers a more accurate label for this thematic group.
This paragraph is sophistry. The addressee of the sonnets is several times described as young, for example in sonnet 22 where “My glass shall not persuade me I am old, / So long as youth and thou are of one date”, or sonnet 54 where the addressee is a “beauteous and lovely youth”, or sonnet 98 which starts “Some say thy fault is youth”. So Grimes’ only point is that there is no evidence that the addressee of these sonnets is a young man specifically. But the people who think that the addressee is a young man do so under the reasonable, if by no means certain, assumption that the addressee of sonnets 18 onwards is the same as the addressee of sonnets 1–17, who seems to be a man, most clearly in sonnet 9, “Is it for fear to wet a widow’s eye, / That thou consum’st thy self in single life?”
Moving on, if Grimes can convince us that the addressee of neighbouring sonnets is the poet’s talent, then maybe we can read this back into sonnet 30. But Grimes makes no attempt to do so here, making the essay completely unconvincing. Sonnet 30 is generic, so all sorts of things could potentially be read into the “dear friend”, but without seeing an actual argument, we have no reason to agree with Grimes that “Shakespeare’s talent” is a useful way to read this phrase.