libfuse3-dev is a virtual package?

["Theodore Ts'o" <tytso@mit.edu>]

So this is weird.  I can't install libfuse3-dev on my buster system:

# apt install libfuse3-dev
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package libfuse3-dev is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'libfuse3-dev' has no installation candidate

Apt seems to think it is a virtual package:

# apt show libfuse3-dev
Package: libfuse3-dev
State: not a real package (virtual)
N: Can't select candidate version from package libfuse3-dev as it has no candidate
N: There is 1 additional record. Please use the '-a' switch to see it
N: No packages found
# apt show -a libfuse3-dev
Package: libfuse3-dev
Version: 3.4.1-1
Priority: optional
Section: libdevel
Source: fuse3
Maintainer: Laszlo Boszormenyi (GCS) <gcs@debian.org>
Installed-Size: 668 kB
Depends: libfuse3-3 (= 3.4.1-1), libselinux-dev
Suggests: fuse
Homepage: https://github.com/libfuse/libfuse/wiki
Tag: devel::library, role::devel-lib
Download-Size: 128 kB
APT-Sources: https://mirrors.kernel.org/debian buster/main amd64 Packages
Description: Filesystem in Userspace (development) (3.x version)
 Filesystem in Userspace (FUSE) is a simple interface for userspace programs to
 export a virtual filesystem to the Linux kernel. It also aims to provide a
 secure method for non privileged users to create and mount their own filesystem
 implementations.
 .
 This package contains the development files.

But as near as I can tell, it's a real package:

	https://packages.debian.org/buster/libfuse3-dev

Help?

					- Ted