ISO8601 is a collection of different formats, and using a space instead of a ‘T’ is one of the allowed variations. I’m not sure anything implements the full spec perfectly.
> The character [T] shall be used as time designator to indicate the start of the representation of the time of day component in these expressions. The hyphen [-] and the colon [:] shall be used, in accordance with 4.4.4, as separators within the date and time of day expressions, respectively, when required.
> NOTE By mutual agreement of the partners in information interchange, the character [T] may be omitted in applications where there is no risk of confusing a date and time of day representation with others defined in this International Standard.
They then show examples which clearly show that they mean you can not-include the T, but you CANNOT substitute T for a space.
Unless I am incorrectly reading the document or unaware of a further section indicating the further allowance of substituting a T for a space, you cannot swap T for space according to the standard.
1 - https://www.loc.gov/standards/datetime/iso-tc154-wg5_n0038_i...
You can compare the formats here: https://ijmacd.github.io/rfc3339-iso8601/
The amount of handwaving in ISO8601 could turn a windmill, though in this respect RFC3339 is not much better. The ABNF clearly shows "T" (case-insensitive) as the only separator, but immediately afterward gives us this:
> NOTE: ISO 8601 defines date and time separated by "T". Applications using this syntax may choose, for the sake of readability, to specify a full-date and full-time separated by (say) a space character.
Separated by (say) whatever the hell you want apparently. I'm getting bruises on my face from all the palming.