In the 9.6 release cycle, https://groups.google.com/g/sage-release/c/GOGWk66zaCQ/m/M_jQiOjaAAAJ:
Users/developers who like to continue using the Cygwin port are asked to step up to investigating and fixing these bugs on Cygwin. Otherwise, it is unlikely that we'll be able to continue offering the Cygwin port.

This has not happened, and on top of the problems at runtime in Sage 9.6, there are now several issues that prevent a successful installation on Cygwin.

To avoid user frustration (2022 sage-devel posts: https://groups.google.com/g/sage-devel/c/_z1Fv_OH1mk/m/nYZFkRi7AQAJ, https://groups.google.com/g/sage-devel/c/JNDU9Fa0Ths/m/2zDrFH91AQAJ, https://groups.google.com/g/sage-devel/c/qB8CU0JdC1I/m/jFUeImPZAAAJ, https://groups.google.com/g/sage-devel/c/pXN2B1NKpsQ/m/Vbn0HHN_FQAJ), we update README.md and manuals to reflect reality.

Announcement:

• https://trac.sagemath.org/wiki/ReleaseTours/sage-9.7#Sage9.7doesnotsupportCygwinuseWindowsSubsystemforLinuxinstead
• https://groups.google.com/g/sage-devel/c/jDsOz7qWwV0

CC: @jhpalmieri @tscrim @slel

Component: porting: Cygwin

Author: Matthias Koeppe

Branch/Commit: cd72e6b

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/34301