I got an email from Apple, "Your Developer ID Installer Certificate will no longer be valid in 30 days". So I went to my certificates page on developer.apple.com, and I see the attached photo.
Basically, yes, I have a Developer ID Installer Certificate that expires 2023/07/01; but I also have one that expires 2025/12/08, and one that expires 2026/01/09, and one that expires 2026/12/15, and another that expires 2026/12/16! Why do I have all these certificates? I have no idea. There is a "+" button to add a new one; but given that I already seem to have ones that won't expire for several more years, do I need to? There does not seem to be a "-" button, or any way to clear out this cruft.
I then recalled that perhaps I have managed my certificates in Xcode in the past, not on this page (or maybe I have done both, at different times?). So I went to Xcode, and things seem to be rather a mess there too, but in a different way (second image attached).
Here, I seem to have lots of stale certificates that are in gray and say "Not in Keychain" – how do I clear those out? Again there does not seem to be a "-" button. And the newer ones that I saw on developer.apple.com do not seem to be listed here, maybe – it's hard to compare, though, because on developer.apple.com it shows the expiration date but not creation date, whereas in Xcode it shows creation date but not expiration date.
What should I do? Note that I am not a member of multiple different teams, or anything like that; I'm a solo developer. This stuff is really confusing and does not seem to be well-documented anywhere that I have found. Am I just being dense?