ED endings: Adjective or Past Participle in Perfect Tenses, Passive Voice and after To Be? [duplicate]
Linguists don't agree as a group about how to analyze participles, adjectives, and verbs. All linguists agree that there are some words with the form of participles that are adjectives: for example, "bored" in the phrase "very bored". These adjectives with the form of participles can be analyzed as derived words; accordingly, one term for them is "departicipial adjectives", to express the idea that they are adjectives that come from participles.
But there is disagreement about whether participles are adjectives when they function as inflected forms of verbs.
For example, in "Word-class-changing inflection and morphological theory"(1996) Martin Haspelmath argues that participles are adjectives produced from verbs by word-class-changing inflection, while acknowledging that it is "widespread" to view them as verbs (p. 49).
The "be __ed" construction is ambiguous in general: it can either involve a departicipial adjective, or a participle as an inflected form. The participle would generally be interpreted as an inflected form when the clause has a dynamic as opposed to a stative sense: if ""The wall is painted" is used to describe a current action (a fairly uncommon use of the simple present tense in English) then "painted" would be a participle (an inflected form of a verb, which might or might not be an adjective depending on your point of view).
In "The speaker wants to be transferred", the word "transferred" seems to have a dynamic sense, so I would say that it is a participle and not a departicipial adjective in this sentence.