Strangely, these limitations don't seem to have been present on the European platforms. (Although I've never bought shares in an IPO myself, so I'm not certain about this.)

e.g. with https://www.nordnet.dk/kampagner/ipo/spacex for Denmark.

The minimum is 1 share (~$135), the FAQ on "when can I sell" says "Once trading begins in SpaceX, you can sell your shares at the current market price, which can be both higher and lower than the IPO price."