Unfortunately it's not easy. In the US specifically banks don't generally offer APIs or keys to access them to individuals and you have to go through an aggregator like Plaid (which is what I want to avoid).

However, most banks do send alert emails when something is charged to a credit/debit card. Meli connects to your inbox read-only via OAuth (Google and Microsoft) or IMAP for other providers and reads those emails on your Mac.

Of course there are limitations to this approach, you only get access to the data that is available in those emails like merchant, amount, date and account.

Which banks are you interested in? Are you based in the US?