Happened after a windows update for me. I've tried to restore them, inspect the database where they should be, but they were already gone. Maybe if you have a system backup, you can find yours!
I've found this random tutorial how to mass create Edge search engines by editing the Edge database https://jeffhandley.com/2022-10-17/custom-search-engines
if you want to store your search engines in a separate file in the future
I use the URL "https://www.google.com/search?q=site:ycombinator.com+%s" to search content from HN, and "https://www.google.com/search?q=site:reddit.com+%s" to search on Reddit. I also have "https://www.npmjs.com/package/%s" to directly go to a package page on npm.