Find the answers to your questions.

SapMachine is a build of the OpenJDK, maintained and supported by SAP and enhanced with enterprise features. It provides a free and open-source implementation of the Java Platform, Standard Edition (Java SE).
New SapMachine major releases appear twice a year, following the OpenJDK release train. The detailed schedule can be found at OpenJDK's JDK Project. While each major release is usually only supported for half a year until the next major release is out, every other year one major release is designated as Long-Term Support (LTS) and will be maintained for a longer period. For supported major versions, there will be an update releases every quarter of a year, as documented in OpenJDK's JDK Update Project. How this maps to SapMachine can be seen on the Maintenance and Support page.
SAP is member of the OpenJDK Vulnerability Group, a secure, private forum in which trusted members of the OpenJDK Community receive reports of vulnerabilities in OpenJDK code bases, review them, collaborate on fixing them, coordinate the release of such fixes, and share the security fixes before release. Therewith SapMachine can build and test upcoming critical patch updates before these are made public. SAP internal colleagues can take part in these tests to ensure that their products are secure on day one after critical patch updates will be released to everyone.
Security updates, also known as Critical Patch Updates (CPU), are released every quarter of a year for all active versions of SapMachine. The release is scheduled for the Tuesday closest to the 17th day of January, April, July and October.
The list of current supported platforms is available on the Maintenance and Support page.
Information can be found on the Certification and Java Compatibility page.
All known differences are detailed in the Features of SapMachine page.
Yes. The SapMachine team is actively contributing to the OpenJDK. Team individuals are holding different project and group related roles, such as Project Lead, Reviewer or Committer. We contribute new features, but also provide bug fixes and are maintainers of the JDK updates projects.
SapMachine debug symbols are available as separate binaries in the release section on GitHub (e.g. for SapMachine 25.0.4 on Linux-x64 the correct archive would be sapmachine-jdk-25.0.4_linux-x64_bin-symbols.tar.gz).
Download the archive matching your architecture, extract it and copy the content of the bin and lib folder to the same directory in the root directory of your SapMachine installation.