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

Calculating dependencies ... done!
Dependency resolution took 1.63 s (backtrack: 0/20).

[ebuild     U  ] dev-libs/glib-2.88.3:2::gentoo [2.84.4-r2:2::gentoo] USE="dbus elf mime xattr -debug -doc -introspection (-selinux) -static-libs -sysprof -systemtap -test -utils" 5678 KiB
[blocks B      ] <dev-util/gdbus-codegen-2.88.3 ("<dev-util/gdbus-codegen-2.88.3" is soft blocking dev-libs/glib-2.88.3)

Total: 1 package (1 upgrade), Size of downloads: 5678 KiB
Conflict: 1 block (1 unsatisfied)

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

  (dev-util/gdbus-codegen-2.84.4:0/0::gentoo, installed) pulled in by
    >=dev-util/gdbus-codegen-2.80.5-r1 required by (gnome-base/dconf-0.40.0:0/0::gentoo, installed) USE="-gtk-doc -test"

  (dev-libs/glib-2.88.3:2/2::gentoo, ebuild scheduled for merge) pulled in by
    =dev-libs/glib-2.88.3
    >=dev-libs/glib-2.38:2[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/glib-2.38:2[abi_x86_64(-)]) required by (media-libs/harfbuzz-12.3.2:0/6.0.0::gentoo, installed) USE="cairo glib graphite truetype -debug -doc -experimental -icu -introspection -test"
    >=dev-libs/glib-2.26:2 required by (dev-util/desktop-file-utils-0.28:0/0::gentoo, installed) USE=""
    dev-libs/glib:2 required by (x11-misc/shared-mime-info-2.4-r3:0/0::gentoo, installed) USE="-test"
    >=dev-libs/glib-2.34.3:2[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/glib-2.34.3:2[abi_x86_64(-)]) required by (x11-libs/cairo-1.18.4-r1:0/0::gentoo, installed) USE="X glib (-aqua) (-debug) -gtk-doc -lzo -test"
    >=dev-libs/glib-2.44.0:2 required by (gnome-base/dconf-0.40.0:0/0::gentoo, installed) USE="-gtk-doc -test"
    >=dev-libs/glib-2.84.4 required by (dev-util/gdbus-codegen-2.84.4:0/0::gentoo, installed) USE="" PYTHON_SINGLE_TARGET="python3_13 -python3_11 -python3_12 -python3_14"


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