Thank you very much.

IMDB https://www.imdb.com/name/nm0003433/ Carl Theodor Dreyer (1889–1968) - Writer | Director | Editor
WIKI https://en.wikipedia.org/wiki/Carl_Theodor_Dreyer Carl Theodor Dreyer
Source https://www.carlthdreyer.dk/en/carlthdreyer/gallery/photos-and-posters/portraits Carl Th. Dreyer
Add Bio Wiki
Add 6 images

About what name to use, see here: https://www.themoviedb.org/bible/people

1 ... the last name used by a living person.
2 For deceased folks, we usually use the name they are most often credited as. An exception can be made if they are best known by a different name.

The only source I know to evaluate and / or quantify the names that were used is IMDB.
And it seems that the most used was Carl Theodor Dreyer.
It is also better to unify, use the same from IMDB and Wikipedia.
Carl Theodor Dreyer

TIP: If you want to force the line break, click Space 2 times and then click Enter. Just Space > Space > Enter.

My curiosity.
What is your native language? Danish (da-DK)?

That's fair enough, I suppose. That said, he's credited as Carl Th. Dreyer on his official site, which is run by The Danish Film Institute (Det Danske Filminstitut). https://www.carlthdreyer.dk/en

For whatever it may be worth, I just now checked my Criterion DVD of Dreyer's La passion de Jeanne d'Arc (The Passion of Joan of Arc) (1928), and it repeatedly (on the cover [front and back], as well as in the insert) presents his name as Carl Th. Dreyer. I've, throughout the years, seen his name presented fully spelled out, as well as the abbreviated-middle-name way - but usually the abbreviated way.

Following is how the TCM site presents about him: http://www.tcm.com/tcmdb/person/361400%7C26985/Carl-Th-Dreyer/

Meanwhile, however, a boxed Criterion Dreyer set presents his name fully spelled out (on the cover, at least): https://www.criterion.com/boxsets/254-carl-theodor-dreyer-box-set (FYI: My Criterion The Passion of Joan of Arc DVD is the one that Criterion sells separately - not in a boxed set.)