YouTube comment formatting
YouTube comments have their own simple markup, so you do not need a generator there:
*bold* with one asterisk on each side
_italic_ with one underscore on each side
-strikethrough- with one hyphen on each side
The symbols must touch the text, and the formatting appears once the comment is posted. If it does not work, check for a space just inside the symbols.
You type
*Timestamp:* 4:12 is where the fix starts
Titles, descriptions and channel names
Comment markup does not work in titles, descriptions or your channel name. Those fields show exactly the characters you type.
That is where bold Unicode letters help. Paste a bold label into a description to separate chapters, links or credits, for example a bold "Links" or "Chapters" heading. Your channel description has a 1,000-character limit, and bold letters count toward it.
Be careful with titles. YouTube search reads plain letters, so a word written in bold Unicode will not help the video be found for that word.
Readability and other platforms
Bold Unicode letters are separate symbols, so screen readers may not read them as words. Use them for short labels, never for the information a viewer needs.
If you post the same text to X, most of these letters count as 2 characters there.