Use ISO time and date format in KDE 5

I've been using Dolphin for organising pictures. I would like to see the modification time and date displayed in ISO format. It is easier to read for me. I used to be able to configure that in KDE 4:

In KDE5 the widget has been replaced by this:

Is there a way to configure this in KDE5?

I find en_SE to be fully ISO-compliant: YYYY-MM-DD HH:MM (24h)

Whereas for me en_DK uses DD/MM/YYYY HH.MM (24h) which is not ISO compliant both in the date order (it's simply a western europe order) and in the time separator.

en_CA uses YYYY-MM-DD hh:MM (12h) likewise close but uses AM/PM rather than 24h.

Tested on KDE Plasma 5.11.3, running on Arch Linux.

EDIT 2021-11-08: If en_SE is not present in your system, in the comments to this answer Kael Watts-Deuchar has steps to create it manually.

No that is impossible. Is is not possible to manually set the formats like it was possible in KDE4. You always have to choose a locale for each category (Number, Time, Currency, Units, Collation)

Unfortunately installing a more standards compliant locale (like en_DK or en_NL) does not help. KDE5 uses its own list of locales, ignoring the system locales.

For the desktop clock you can set the date and time format apart from the system format in newer version of KDE 5.