The galera package itself does not need "openssl/engine.h" to compile.

There are only two instanced of that include:

1) File: "asio/asio/ssl/detail/openssl_types.hpp", necessary for galera itself to build
Which contains coorectly conditioned:
|  #if !defined(OPENSSL_NO_ENGINE)
|  # include <openssl/engine.h>
|  #endif // !defined(OPENSSL_NO_ENGINE)

2) File: "galera-26.4.19/galerautils/tests/gu_asio_test.cpp", necessary for galera 'galerautils' tests to build

which does not have the include inside a condition, as the code requires it in any case.

==

As a workaround, disable build of the 'galerautils' tests, until
the openssl engine functionality is correctly removed from it.

--- galera-26.4.19/galerautils/CMakeLists.txt	2024-08-20 15:56:58.821943102 +0200
+++ galera-26.4.19/galerautils/CMakeLists.txt_patched	2024-08-20 15:57:07.027849238 +0200
@@ -3,4 +3,4 @@
 #
 
 add_subdirectory(src)
-add_subdirectory(tests)
+#add_subdirectory(tests)