Learn English – Singular and plural sentence

The correct use changes depending on the sentence:

Do you have any idea how to do this?
Do you have any idea what to do?
Do you have any ideas for me?
Do you have any ideas for how to do this?

It seems that, if the singular or plural noun (idea) is directly connected by a subordinating conjuction (how / what / where / which / that), you use the singular; if it's modified by a prepositional phrase (for...) or by nothing at all, you use the plural.

Without using all that grammar jargon, I'd say use the singular if it's followed by how, what, that, who, whom, whose, which, etc, and use the plural otherwise.

Oxford Learners' Dictionary and Cambridge English Dictionary both provide examples illustrating both the singular and plural verb-use cases. If you are using "majority" to indicate a group of multiple units, use the plural verb. If you are using "majority" to indicate a single collective group, use the singular verb. "A majority" would normally indicate a single collective group, hence, requiring the singular verb.

While the choice is quite subjective, in your example, I would use the plural verb "recommend" since the intent seems to be to stress on multiple sources of the recommendation.