Google deprecated rel=prev/next as a ranking signal in 2019 but still uses it for discovery. More importantly: the "canonical-to-page-1" anti-pattern (every paginated page claims /page-1/ as canonical) de-indexes everything beyond page 1.
Read the story behind this tool: Why Your Blog Has 200 Posts But Only Page 1 Is Indexed →
Enter page 1 URL. The tool follows rel=next up to 10 pages to validate the chain.