Constant STRICT_BOOT_WITHOUT_FSVERITY_HELP 

pub(crate) const STRICT_BOOT_WITHOUT_FSVERITY_HELP: &str = "This boot entry requires fs-verity \
(its composefs= argument has no '?'), but the root filesystem does not support it (for \
example ext4 created without '-O verity'). To boot, select the previous deployment in \
the boot menu, or add '?' right after 'composefs=' (or 'composefs.digest=') in this \
entry's kernel command line, which boots without fs-verity enforcement. To enforce \
fs-verity, reinstall onto a filesystem with fs-verity enabled";

Shown when a strict composefs= boot finds a root filesystem without fs-verity support, e.g. ext4 made without -O verity by another tool.