Data thresholding is GA4 withholding rows when a segment's volume is low, to protect user privacy — showing zeros or a thresholding notice instead of the data.
Why it matters for your earnings
On a niche site, thresholding hides exactly the granular page and segment data you need; the more specific your question, the more likely GA4 refuses to answer it.
Go deeper: Guide: GA4 Limitations