> "Open banking" is kind of a thing with PSD2/PSD3, but in name only. In reality, it's impossible to build anything useful

You mean the step from sandbox to production application, or you're not even getting access to the sandbox itself? I managed to get sandbox access with ease via two separate banks (both Spanish though), with no problems, think it took them one (working) day or something to review my "application". I never tried to get anything into the production environments though, but makes sense they'd be a bit tighter on that tbh.