We're curious about your browser configuration that makes you see this. 🤔
In Settings > General, what user interface language have you chosen and what are your date and time settings?
@Vivaldi My UI language is English (US) and date & time format is "Inherit from operating system". I'm using Ubuntu with GNOME and in the Date & Time settings the only relevant setting that I can see is 24 hour time. Right now the "Long Date" in Vivaldi settings says "Wednesday 14. Januarytpm 2026 16.31.34".
We've tested, but haven't been able to reproduce the bug. However, the devs would still like to look into the issue, so please file a bug report about it on https://vivaldi.com/bugreport/. Include the same information about the setup and settings in the ticket and add other information you think may be relevant. Like do you only see the bug only in the History Manager or also in the Calendar.