Not all iCloud Data is E2E encrypted, most iCloud services actually work on the web if you go to icloud.com. In fact E2E encrypted services are still the exception, not the rule: https://support.apple.com/de-de/HT202303
It's frustrating that Apple does not let users disable iCloud tabs without also disabling bookmarks and the reading list (which I am fine with being synced on US servers).
Workaround: Toggle mobile Safari into private browsing mode and use apps for everything that needs a login, use private browsing mode most of the time on macOS :/
It's frustrating that Apple does not let users disable iCloud tabs without also disabling bookmarks and the reading list (which I am fine with being synced on US servers).
Workaround: Toggle mobile Safari into private browsing mode and use apps for everything that needs a login, use private browsing mode most of the time on macOS :/