You do not type it from a keyboard; you copy it. Press the copy button above and paste it into any app. That is the whole point of Unicode styled letters.
Where can I use the Bold Italic D?
Anywhere text is accepted: Instagram bios, TikTok names, Discord, WhatsApp, gaming profiles and documents. The full Bold Italic alphabet is linked above.
What is the Bold Italic letter D?
It is the letter D rendered as the Unicode character ๐ซ (code point U+1D46B), part of the Bold Italic styled alphabet. It is a single character you can copy and paste anywhere.