I know that banks in Europe are bound by law to follow PSD2, which is a set of guidelines to propose APIs. I found a stackoverflow post to generate the required certificates for that but those are only supposed to be for testing purposes https://stackoverflow.com/questions/50045376/how-to-create-eidas-certificate-with-qwac-and-qsealc-profiles-psd2-specific-att
You can use the PSD2 api to fetch the transactions from your account directly, that would be a lot less troublesome. There is also the woob (formerly weboob) project that has web scraping for a lot of banks (specifically french but also some American ones like amex)
My point was that there is no need to replicate everything everywhere. If the data is replicated a cross 5 instances per region for instance, it’s enough for replication needs. If you self host lemmy and subscribes to large communities on your instance, you can quickly overload your server. We need activity pub to be more lightweight if we want smaller instances to thrive.