This is a quick post on how to fix this error with the steam overlay on gentoo:

./steamwebhelper: symbol lookup error: /usr/lib64/libfreetype.so.6: undefined symbol: hb_ot_tags_from_script_and_language

This has to do with an error with freetype, a font rendering service. Chances are if you are seeing this error in the terminal when launching steam nothing is rendering either. Pages most likely are a black or grey. To fix this issue, you have to mask the latest version of freetype. Modify your package.mask file as shown:

#File: /etc/portage/package.mask =media-libs/freetype-2.11.0

You might also have to add this to your package.use when attempting to recompile freetype

#File: /etc/portage/package.use/media-libs >=media-libs/freetype-2.10.4 harfbuzz

Recompile and steam should be working. Hope this helped with this more obscure error!