These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 3.12 s (backtrack: 3/20).

[ebuild  N     ] dev-libs/libelf-0.8.13-r4::gentoo  USE="nls -debug" 146 KiB
[ebuild     UD ] virtual/libelf-2-r1:0/0::gentoo [3-r1:0/1::gentoo] 0 KiB
[blocks B      ] dev-libs/elfutils ("dev-libs/elfutils" is soft blocking dev-libs/libelf-0.8.13-r4)
[blocks B      ] dev-libs/libelf ("dev-libs/libelf" is soft blocking dev-libs/elfutils-0.194)

Total: 2 packages (1 downgrade, 1 new), Size of downloads: 146 KiB
Conflict: 2 blocks (2 unsatisfied)

!!! Multiple package instances within a single package slot have been pulled
!!! into the dependency graph, resulting in a slot conflict:

virtual/libelf:0

  (virtual/libelf-2-r1:0/0::gentoo, ebuild scheduled for merge) USE="" pulled in by
    =virtual/libelf-2-r1 (Argument)

  (virtual/libelf-3-r1:0/1::gentoo, installed) USE="" pulled in by
    virtual/libelf:0/1= required by (dev-libs/glib-2.84.4-r2:2/2::gentoo, installed) USE="dbus elf mime xattr -debug -doc -introspection (-selinux) -static-libs -sysprof -systemtap -test -utils"
                  ^^^^^                                                                                                                                                                                                                                                                                                                                                                                                                                                                      


!!! The slot conflict(s) shown above involve package(s) which may need to
!!! be rebuilt in order to solve the conflict(s). However, the following
!!! package(s) cannot be rebuilt for the reason(s) shown:

  (dev-libs/glib-2.84.4-r2:2/2::gentoo, installed): ebuild is masked or unavailable


It may be possible to solve this problem by using package.mask to
prevent one of those packages from being selected. However, it is also
possible that conflicting dependencies exist such that they are
impossible to satisfy simultaneously.  If such a conflict exists in
the dependencies of two different packages, then those packages can
not be installed simultaneously. You may want to try a larger value of
the --backtrack option, such as --backtrack=30, in order to see if
that will solve this conflict automatically.

For more information, see MASKED PACKAGES section in the emerge man
page or refer to the Gentoo Handbook.


 * Error: The above package list contains packages which cannot be
 * installed at the same time on the same system.

  (dev-libs/elfutils-0.194:0/0::gentoo, installed) pulled in by
    >=dev-libs/elfutils-0.176-r1:= required by (dev-util/debugedit-5.3:0/0::gentoo, installed) USE="-test -verify-sig"
    >=dev-libs/elfutils-0.155-r1:0/0[abi_x86_32(-)?,abi_x86_64(-)?,abi_x86_x32(-)?,abi_mips_n32(-)?,abi_mips_n64(-)?,abi_mips_o32(-)?,abi_s390_32(-)?,abi_s390_64(-)?] (>=dev-libs/elfutils-0.155-r1:0/0[abi_x86_64(-)]) required by (virtual/libelf-3-r1:0/1::gentoo, installed) USE=""
    dev-libs/elfutils[debuginfod(-)] required by (sys-devel/binutils-2.46.0:2.46/2.46::gentoo, installed) USE="(cet) debuginfod nls pgo plugins zstd -doc -gprofng -hardened -multitarget -static-libs -test -vanilla -xxhash"
    >=dev-libs/elfutils-0.176-r1:0/0= required by (dev-util/debugedit-5.3:0/0::gentoo, installed) USE="-test -verify-sig"

  (dev-libs/libelf-0.8.13-r4:0/0::gentoo, ebuild scheduled for merge) pulled in by
    >=dev-libs/libelf-0.8.13-r2:0/0[abi_x86_32(-)?,abi_x86_64(-)?,abi_x86_x32(-)?,abi_mips_n32(-)?,abi_mips_n64(-)?,abi_mips_o32(-)?,abi_s390_32(-)?,abi_s390_64(-)?] (>=dev-libs/libelf-0.8.13-r2:0/0[abi_x86_64(-)]) required by (virtual/libelf-2-r1:0/0::gentoo, ebuild scheduled for merge) USE=""


For more information about Blocked Packages, please refer to the following
section of the Gentoo Linux x86 Handbook (architecture is irrelevant):

https://wiki.gentoo.org/wiki/Handbook:X86/Working/Portage#Blocked_packages