Anywhere text is accepted: Instagram bios, TikTok names, Discord, WhatsApp, gaming profiles and documents. The full Small Caps alphabet is linked above.
What is the Small Caps letter X?
It is the letter X rendered as the Unicode character x (code point U+78), part of the Small Caps styled alphabet. It is a single character you can copy and paste anywhere.
How do I type x on my phone or computer?
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.