Don't think so - the KPI formatting is preset, and there is very little that can be tweaked. If it's important to make the label bold, then you can revert back to the Text & image chart - it can do almost everything that is possible with KPI (except for the "Link to sheet"), albeit with a bit more tinkering required.
I have similar question on KPI label font size, but you answered seems good to use Text&image chart, but can we do value formatting such decimal suppress, or changing to Money format or % . I hope you or some can see this question and answer to my question. Thank you so much.
The KPI object has a number of formatting advantages over a Text&Image chart, at the price of less flexibility. For example, the KPI object will automatically scale your amounts to the appropriate level (thousands, millions, etc...)
In the Text&Image chart, you need to format your texts properly - you can do it using the num() function, however you won't be able to arrange an automatic scaling as easy as it's implemented in the KPI object.
So, pick your poison - either live with the formatting options that are pre-packed into the KPI object, or format your texts manually in the Text and image chart.