TYPO3 Core

any hints how to reproduce it? CR seems easy, but would like to give "verified" vote too.

Tymoteusz Motylewski wrote in #note-2:

any hints how to reproduce it? CR seems easy, but would like to give "verified" vote too.

I found this by upgrading my extension to v11. I don't know if you can find an error in TYPO3 itself.
But this is definetely wrong if you compare this with version 10.4, where the typeof check was still present:

    const $dateTimeFields = $(selector || this.fieldSelector).filter((index: number, element: HTMLElement): boolean => {
      return typeof $(element).data('DateTimePicker') === 'undefined';
    });