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

Calculating dependencies ... done!
Dependency resolution took 1.70 s (backtrack: 0/20).

[ebuild  N     ] net-libs/wandio-4.2.6:0/6::gentoo  USE="bzip2 http zlib -lz4 -lzma -lzo -test -zstd" 16781 KiB
[ebuild     U  ] app-text/doxygen-1.18.0-r1::gentoo [1.16.1::gentoo] USE="dot* -clang -debug -doc -doxysearch -gui -test" LLVM_SLOT="22* -18 -19 -20 -21*" 9674 KiB
[ebuild  N     ] net-libs/libtrace-4.0.28::gentoo  USE="ncurses -doc -numa" 3651 KiB
[ebuild  N     ] net-libs/libflowmanager-3.0.0-r1:0/3::gentoo  396 KiB
[ebuild  N     ] net-libs/libprotoident-2.0.14_p1:0/2::gentoo  USE="-static-libs -tools" 536 KiB

Total: 5 packages (1 upgrade, 4 new), Size of downloads: 31037 KiB

The following USE changes are necessary to proceed:
 (see "package.use" in the portage(5) man page for more details)
# required by net-libs/libtrace-4.0.28::gentoo
# required by net-libs/libflowmanager-3.0.0-r1::gentoo
# required by net-libs/libprotoident-2.0.14_p1::gentoo
# required by =net-libs/libprotoident-2.0.14_p1 (argument)
>=app-text/doxygen-1.18.0-r1 dot