Hello, in the attached images are two cases I noticed where `display-fill-column-indicator-mode' causes display bugs. First case is with faces that use the :overline or :underline property, the lines will extend fully towards the indicator. Second case is with `company-mode' when there's no text entered and the completion dialog pops up which display-fill-column-indicator-mode treats like ordinary text.

In GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.10, cairo version 1.16.0)

System Description: Debian GNU/Linux bullseye/sid

Configured using:
 'configure 'CFLAGS=-march=native -O2 -pipe -fstack-protector-strong
 -fno-plt' --prefix=/home/drot/.local
 '--program-transform-name=s/^ctags$/ctags.emacs/' --with-cairo
 --with-modules --enable-link-time-optimization --disable-gcc-warnings'

Configured features:
XPM JPEG TIFF GIF PNG RSVG CAIRO SOUND GPM DBUS GSETTINGS GLIB NOTIFY
INOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF
ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD
JSON PDUMPER LCMS2 GMP