Your questions about SoFi Hong Kong are answered here

You can only trade fractional shares with “Fractional Shares Order”, which has similar characteristic to Market Order but except that it will not be executed immediately. The securities within the Fractional Shares collection are also available for whole share trading. To buy one share, you can tap on “More Order Types” and place a Market Order, Good Till Date (GTD) or Limit Order (LO).