How long is an SAP S/4HANA version in mainstream support, and what's SAP's long-term commitment?

Which PAM tab shows valid upgrade source and target releases, e.g. that you can reach S/4HANA 2022?

What is a support package, and how does it relate to the components of the software stack?

When mainstream maintenance for a release ends, what option keeps you supported, and at what cost?

What's the difference between a support package stack (SPS) and a feature package stack (FPS)?

In PAM, how do you find the minimum SAP HANA version and supported OS for S/4HANA?

When can a Feature Package Stack replace a Support Package Stack, and what's the catch with its new features?