For schema.org it is valid because they allow both date and datetime values for the datePublished property, see https://schema.org/datePublished . They refer to ISO_8601 for both, and for dates without time the provided format is valid, see e.g. https://en.wikipedia.org/wiki/ISO_8601 .

However, Google seems to expect datetime values, and those require the time and timezone part, see https://schema.org/DateTime .

So I think it should be fixed to make Google happy.

When not using the manually entered schema.org data for an article but the automatically generated one (there are 2 switches for that in the options of the "Content - Joomla" plugin), I get valid datetimes for dateCreated and dateModified, i.e. with time and time zone. So it seems to be only an issue when using manually entered data.

@richard67
Thank, what do u mean with:
"there are 2 switches for that in the options of the "Content - Joomla" plugin"

@Mich-es In the options (settings) of the content plugin "Content - Joomla" are 2 switches, one for Articles and one for Contacts. When a switch is switched on, schema.org data is added based on article title and so on like it was in Joomla 4 with the html markup. Don't ask me now for the labels of these switches, but you will easily find them when editing the "Content - Joomla" plugin's option.

So what should the format be?
is google only happy with this? 2023-10-22T07:07:59−07:00

if yes then we need a new SchemaorgPrepareDateTimeTrait more or less a copy of SchemaorgPrepareDateTrait with the full datetime string and of course changed where it should be used.

2023-10-22T07:07:59−07:00

The time zone part is optional, and with UTC times we could use 2023-10-22T07:07:59Z.

But the time part Thh:mm:ss is not optional for Google, it seems, i.e. they only accept datetime and not date like schema.org does.