What to run
Open SSL Expiry Checker. The result is from Cloudflare. It reads the peer certificate: issuer, expiry, and days left. It does not grade the whole TLS config.
How to read the result
Read the issuer, not-after, and days left.
Days left under 14 is urgent. Under 30 is the usual renewal window.
The check is the certificate Cloudflare sees on that host and port, not every certificate behind a load balancer.
What to open next
Open DNS Lookup for A and AAAA if you suspect the name points at the wrong machine. DNS Lookup is DNS-over-HTTPS from the browser and does not follow CNAMEs.
Open Is This Website Down if TLS will not complete. That result is from Cloudflare.