In the past, the API that sevdesk exposes allowed for creation of accounts with currencies that differ from EUR, see here. On July 4, 2024, sevdesk announced that the account creation API endpoints were replaced with a new interface. The old endpoints were removed on September 17, 2024.
These new endpoints, createFileImportAccount and createClearingAccount, directly mimic the functionality that is exposed in the web frontend of sevdesk. In particular, either a clearing account can be created that can not be used for importing transaction, or a new account will be created based on a bank integration, CSV file, or a MT940 file. I tried to create USD accounts with both a CSV and a MT940 file containing USD transactions. In this case, sevdesk ignores the currency and blindly assumes EUR, which in the case of MT940 even disregards the standard.
From my POV, existing non-EUR accounts can still be used, but no new non-EUR accounts can be added.