A lot of settlement in financial markets is still pretty slow. That’s a big reason why there was so much fintech interest in blockchain.

You may be thinking of high frequency trading. In that case, traders interact directly with an exchange - e.g. via direct market access[1] - so it’s a pre-established two-party interaction. There’s no particular technical difficulty with making that fast. Usually, slow transaction times are a consequence of the structure of the market, not a technical issue particularly.

[1] https://corporatefinanceinstitute.com/resources/career-map/s...