If it is the Paragraph Style dialogue then I can’t enter anything in there on Windows 11, LO 6.2.8.2, 7.3.5.2, & 7.4.0.3
If you have some text in a document and select a couple of paragraphs, then click Format > Paragraph (that is NOT style dialogue) and enter a word, for example Zebra, then you will see what Zebra would look like in drop caps. If you then OK the dialogue then the first 5 letters (number of letters in Zebra) of the paragraphs become drop caps and Zebra is not shown.
Oddly, this is not what Help implies: Enter the text that you want to display as drop caps instead of the first letters of the paragraph.
but it seems to work as I expect.