Please see the Rambam Hilchos Malachim. Anything not mentioned by the Rambam is not al pi halacha and will not necessarily happen. The Rambam describes a very natural process of the Messianic redemption. If someone will not accept a Messianic candidate to some extent without him already building the Bais Hamikdosh, or waiting for all manner of miraculous signs (which the Rambam says will not necessarily happen), then Moshiach cannot come according to that person in the way described by the Rambam. Such a worldview is kefira.
My comments have nothing to do with mine or anyone’s beliefs regarding the messianic claims or identities of any individual. I am mere commenting on a heretical comment above.
Rambam writes in Hilchos Melachim
ואם יעמוד מלך מבית דויד הוגה בתורה ועוסק במצות כדויד אביו כפי תורה שבכתב ושבעל פה ויכוף כל ישראל לילך בה ולחזק בדקה וילחם מלחמות ה’ הרי זה בחזקת שהוא משיח
According to the false logic above, no candidate would even get to even Chezkas Moshiach because as soon as he tried to rally support for his cause you would have people saying, “I won’t believe you are Moshiach until AFTER you build the Bais Hamikdash.”
II would hope that l’chol hapachus if one of the Gedolei HaTorah was a Ben David and claimed to be a messianic candidate that someone wouldn’t laugh and be dismissive because if so then they don’t really believe it is possible for Moshiach to come.
And again, I repeat, according to Halacha there is no need for an announcement by Eliyahu HaNavi, Moshiach ben Yosef, no flying eagles or men on donkeys etc etc etc.