𝐔𝐧𝐢𝐜𝐨𝐝𝐞 𝐡𝐚𝐬 𝐜𝐡𝐚𝐫𝐚𝐜𝐭𝐞𝐫𝐬 𝐭𝐡𝐚𝐭 𝐥𝐨𝐨𝐤 𝐬𝐢𝐦𝐢𝐥𝐚𝐫 𝐭𝐨 𝐟𝐨𝐫𝐦𝐚𝐭𝐭𝐞𝐝 𝐭𝐞𝐱𝐭.

𝗨𝗻𝗶𝗰𝗼𝗱𝗲 𝗵𝗮𝘀 𝗰𝗵𝗮𝗿𝗮𝗰𝘁𝗲𝗿𝘀 𝘁𝗵𝗮𝘁 𝗹𝗼𝗼𝗸 𝘀𝗶𝗺𝗶𝗹𝗮𝗿 𝘁𝗼 𝗳𝗼𝗿𝗺𝗮𝘁𝘁𝗲𝗱 𝘁𝗲𝘅𝘁.

𝑈𝑛𝑖𝑐𝑜𝑑𝑒 ℎ𝑎𝑠 𝑐ℎ𝑎𝑟𝑎𝑐𝑡𝑒𝑟𝑠 𝑡ℎ𝑎𝑡 𝑙𝑜𝑜𝑘 𝑠𝑖𝑚𝑖𝑙𝑎𝑟 𝑡𝑜 𝑓𝑜𝑟𝑚𝑎𝑡𝑡𝑒𝑑 𝑡𝑒𝑥𝑡.

𝘜𝘯𝘪𝘤𝘰𝘥𝘦 𝘩𝘢𝘴 𝘤𝘩𝘢𝘳𝘢𝘤𝘵𝘦𝘳𝘴 𝘵𝘩𝘢𝘵 𝘭𝘰𝘰𝘬 𝘴𝘪𝘮𝘪𝘭𝘢𝘳 𝘵𝘰 𝘧𝘰𝘳𝘮𝘢𝘵𝘵𝘦𝘥 𝘵𝘦𝘹𝘵.

𝑼𝒏𝒊𝒄𝒐𝒅𝒆 𝒉𝒂𝒔 𝒄𝒉𝒂𝒓𝒂𝒄𝒕𝒆𝒓𝒔 𝒕𝒉𝒂𝒕 𝒍𝒐𝒐𝒌 𝒔𝒊𝒎𝒊𝒍𝒂𝒓 𝒕𝒐 𝒇𝒐𝒓𝒎𝒂𝒕𝒕𝒆𝒅 𝒕𝒆𝒙𝒕.

𝙐𝙣𝙞𝙘𝙤𝙙𝙚 𝙝𝙖𝙨 𝙘𝙝𝙖𝙧𝙖𝙘𝙩𝙚𝙧𝙨 𝙩𝙝𝙖𝙩 𝙡𝙤𝙤𝙠 𝙨𝙞𝙢𝙞𝙡𝙖𝙧 𝙩𝙤 𝙛𝙤𝙧𝙢𝙖𝙩𝙩𝙚𝙙 𝙩𝙚𝙭𝙩.

(Don't do this: it's _terrible_ for accessibility, as screen readers can't parse these as regular text)

Unicode. E.g. https://unicode-search.net/unicode-namesearch.pl?term=BOLD#:....

These are Unicode characters intended for use in mathematical formulas, not text, so they break all sorts of things. It might make some sense to use them in mathematical Python code (where they do seem to work), but they're hard to type.

Looks like Unicode characters to me.