The Qt v5.15 Community doesn't support OpenSSL 3 by default. You will face some issues at runtime if you attempt to build it with OpenSSL 3. This gist explains how to do it by yourself.
- Apply two attached patches
- Install OpenSSL 3
- Config the Qt with installed OpenSSL like this:
..\configure -prefix h:\mousavi\Qt\5.15.10\win32-msvc2019-x86 -debug-and-release -skip qtwebengine -openssl-runtime OPENSSL_PREFIX="H:\mousavi\OpenSSL-Win32"`