@rebEliezer @menachemShmei
You both seem to have looked into this topic well.
I am aware that shitas HaRambam is that the Beis Hamikdash will be built by people (seemingly Moshiach).
And you brought a source to explain how the “beis Hamikdash of fire” will come down after the physical one is built.
What does the Rambam do with the gemara in Sukkah (also rosh Hashana) that Rabbi Yochanan ben Zakkai forbade eating “chodosh” the entire 16th of Nissan, since there’s a concern that the beis Hamikdosh will have returned and people won’t have found out about it?
The gemara is clear that the beis hamikdosh will come back at night time (or perhaps right before shkiya on the 15th of nissan).
Rashi and Tosfos (and others) point out how the beis hamikdosh will come back at night time, and that’s not a problem since the mitzva to build it during the day only applies to the first batei mikdosh which was built by people; but the third one will come down in fire, and thus can come at night as well.
You’ve explained how the Rambam will learn the medrash about the mikdash of fire; but there’s still the clear issue of rav Yochanan ben Zakkai’s takana.
He is very clear that there’s reason to assume the beis hamikdosh will be present on the 16th of nissan even though there was absolutely no mikdash there when pesach started a day earlier.
This is one of the major sources for those rishonim who argue on the Rambam.
How does he Rambam explain this gemara?
(I’m sure there are mefarshim who address this topic, I just haven’t seen them. You have studied this much more than I have, so maybe you’ve come across the answer?)