We can increase the size, color and back ground of the text, I doubt we can't make it bold or Italic.
For your requirement, you can try increasing the text size and changing the color to darker.
The functionality to bold text is not possible yet within the PI Vision UI.
There are the following enhancement requests to change this functionality:
If I need to achieve it, I will try to create custom symbol.
Previously I tried to change font family... it was fun. (The link is not for the latest version of PI Vision)
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