I apologize ahead of time if this goes in a different area. I have spent the better of 6-8 hours trying to figure out why all of a sudden I could no longer use my openID sign in for Proxmox. I updated proxmox, authelia, rebooted everything, crawled through logs left and right. I finally happened to click on one of the suggestions listed on the Overview page about activating the new Block AI Scrapers and Crawlers option and remembered that I had recently activated that, just about 6-8 hours ago. I turned it off and BAM, now my OpenID sign in is working again.
TL;DR: The new Block AI Scrapers and Crawlers option was giving a 500 error when attempting to use OpenID authentication on Proxmox.