It is the letter B rendered as the Unicode character ʙ (code point U+299), part of the Small Caps styled alphabet. It is a single character you can copy and paste anywhere.
How do I type ʙ 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.
Where can I use the Small Caps B?
Anywhere text is accepted: Instagram bios, TikTok names, Discord, WhatsApp, gaming profiles and documents. The full Small Caps alphabet is linked above.