It means that the writer is frustrated about the capital allocation policies, and are asserting that other shareholders are also frustrated about that. You can use a lot of prepositions there:
share our frustration at Apple's capital allocation policies
share our frustration with Apple's capital allocation policies
share our frustration concerning Apple's capital allocation policies
share our frustration regarding Apple's capital allocation policies
To share an emotion is an idiomatic way of of saying you experience something similar. It comes up a lot - "I share your pain", "perhaps you will share my anxiety", "we all share your concern". When you assert that you share someone's emotion, it's intended to create a sense of empathy and fellow-feeling, to make someone feel heard and understood. It can be used to manipulate people. When used about a third party, as here, it is used to assert that you have a lot of support.