Anywhere text is accepted: Instagram bios, TikTok names, Discord, WhatsApp, gaming profiles and documents. The full Bubble (Circled) alphabet is linked above.
What is the Bubble (Circled) letter X?
It is the letter X rendered as the Unicode character Ⓧ (code point U+24CD), part of the Bubble (Circled) styled alphabet. It is a single character you can copy and paste anywhere.
How do I type Ⓧ 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.