@Eduardo S wrote:
In the sentence "您的外卖可能会晚到一会" what is the function of 到？
In this sentence, 到 is the main verb. As you correctly said, it is used with the meaning of "to arrive".
You are also correct when you say that 可能 is an adverb and 会 an auxiliary verb.
About 会 in "可能会"
It's easy for us English/Italian/Spanish/... speakers to see 会 as a verb used "to indicate future tense", as you said. But it would be a mistake. In this sentence, it means "to be possible, probable, likely, sure". The degree of the possibility is indicated by adverbs like 可能, 一定, etc.:
While it's true that it is often used to indicate a future possibility, it can also indicate a possibility in the past or at the present. Definitely, it is not a verb used "to indicate future tense".
From the book 《现代汉语八百词》: