TikTok captions are read at speed, so styling has to help scanning rather than slow it down. One styled phrase near the start is usually enough.
A Stylish Text Generator gives you bold, italic and script variants in one view. Copy the one that matches the video's tone, then add plain text for the details.
Do not style hashtags; the app may stop recognising them as links.
Written by FontStyle - more at fontstyle.io.