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

Calculating dependencies ... done!
Dependency resolution took 1.69 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-4.0.21::gentoo  USE="ncurses -doc -numa" 3655 KiB

Total: 3 packages (1 upgrade, 2 new), Size of downloads: 30109 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-4.0.21::gentoo
# required by =net-libs/libtrace-4.0.21 (argument)
>=app-text/doxygen-1.18.0-r1 dot