>>107507758
Looks like it only recently got stabilised a month ago. Does 3.4.3 build and install for you?
$ sudo emerge -v1u "~dev-libs/openssl-3.4.3"
If so then you may consider masking 3.5.4 for now in /etc/portage/package.mask. Also file a bug on bugs.gentoo.org because something more complex is clearly going on here.
It could be that if you can build 3.4.3 and update the rest of @world then you can drop the mask afterwards.
Also is Portage up-to-date?
$ sudo emerge -v1u sys-apps/portage