Typically in an IPO, the offering is about 20% of valuation of the company at the first offering. But with a $trillion or more, they will offer say 10% or less.. say $100B in one go is probably what the market can take.. Some banker has to back it up initially and defend that price... the next dump will be about same amount say $100B again but not the same number of shares. The underwriters are not obliged to back $1T and the IPOed company is not obliged to release more shares.

Ultimately the percentage of shares that public will trade is material. say 20% for $100B is quite different from 10% for $100B.