How to retrieve block data?

// Retrieve block details once and use throughout
const block = this.api.blocks.getBlockByIndex(blockIndex);

console.log('Block data:', block.data, 'Block index:', blockIndex);
if (!block || !block.id) {
throw new Error('No valid ID for the current block.');
}

const originalText = block.data?.text; // Using optional chaining for safety
console.log(block);

Block data is undefined, how do I retrieve the contents of a block, such as the text of a paragraph of heading? Or a list content?