> s390 is a 31-bit platform, not a 32-bit platform.

ARM64 only uses 48 bits for the address, but it uses 64-bit CPU words. Usually, we refer to an architecture by its CPU word, 32 or 64 bits. s390 uses 32-bit CPU words, no?

The Wikipedia article says:

"ESA/390 is arguably a 32-bit architecture; as with System/360, System/370, 370-XA, and ESA/370, the general-purpose registers are 32 bits long, and the arithmetic instructions support 32-bit arithmetic. Only byte-addressable real memory (Central Storage) and Virtual Storage addressing is limited to 31 bits."

> s390 packages are still being built for SUSE Linux Enterprise 12 which is still actively supported. I assume the same applies to RHEL LTS releases but I can't verify that as I have no insight into RedHat's internal build system.

Red Hat maintains Fedora and RHEL, none is supporting s390, but both support s390x:

* https://fedoraproject.org/wiki/Architectures
* https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/considerations_in_adopting_rhel_8/architectures_considerations-in-adopting-rhel-8

Note: The correct name is Red Hat ;-)