[NoboruWataya]

In the EU and UK, banks are required to impose onerous security and authentication requirements on third party software before granting account access. The rules are designed to protect consumers from insecure or malicious software but unfortunately a side effect is that open source projects are quite unlikely to be able to comply. The most we can hope for is usually that a bank lets you manually download statements as OFX. HSBC does that for example but some other banks/ credit card providers only give you QIF or CSV.

[Hackbraten]

One commenter mentioned aqbanking, which is open-source and can navigate various kinds of 2FA shenanigans via the FinTS protocol. For example, it communicates to my card reader via USB, and relays the resulting TAN back to the bank server.