> The question is why the missing header was not detected by configure?
We don't test for every 3rd party header we include. If engines were separate from OpenSSL we'd probably probe for it, but this separation is a packager decision and not one from the OpenSSL project.
> The description of this package says so the OpenSSL ENGINE is deprecated?
OpenSSL deprecated the concept of engines in favor of providers in OpenSSL 3.0, but as is common with OpenSSL they are still around and there is a way to keep them running albeit in a limited fashion.
PostgreSQL still support OpenSSL 1.1.1 where engines aren't deprecated, and I expect we will for some time.
