Make a custom block like default paragraph block, so that Enter starts a new block

You can check out the code of the paragraph (and heading) block. It’s open source code !yay! Let it inspire you.

<RichText 
  ...
  onSplit={ ( value ) => {
    if ( ! value ) {
      return createBlock( name );
    }
    return createBlock( name, {
     ...attributes,
     content: value,
    } );
  } }
  onMerge={ mergeBlocks }
  ...
</RichText>