Can't Click Links from Evolution

[Douglas Summers]

(on Linux Mint 18.3, flatpak 0.11.7)

Referencing this site (https://wiki.gnome.org/Apps/Evolution/Flatpak),
I built Evolution 3.28. Other than a few warnings, the build seemed to
go OK. After successfully creating an account, I tried to click on a
link within a message and got this error:

GDBus.Error: org.freedesktop.DBus.Error.ServiceUnknown: The name
org.freedesktop.portal.Desktop was not provided by any .service files.

In the recent past, I was able to build Evolution and never got this
message. I believe that I was using an older version of flatpak, but I
can't be sure (whatever the default version on Fedora 27 is).

Here's my environment variables:
CINNAMON_VERSION=3.6.7
DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-
mAyfAadIq0,guid=db2ca0b3830e7ecd0871f5ba5b099773
DEFAULTS_PATH=/usr/share/gconf/cinnamon.default.path
DESKTOP_SESSION=cinnamon
DISPLAY=:0
GDM_LANG=en_US
GDMSESSION=cinnamon
GJS_DEBUG_OUTPUT=stderr
GJS_DEBUG_TOPICS=JS ERROR;JS LOG
GNOME_DESKTOP_SESSION_ID=this-is-deprecated
GTK_MODULES=gail:atk-bridge
GTK_OVERLAY_SCROLLING=1
HOME=~
LANG=en_US.UTF-8
LANGUAGE=en_US
LOGNAME=me
MANDATORY_PATH=/usr/share/gconf/cinnamon.mandatory.path
OLDPWD=~
PATH=~/bin:~/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/b
in:/sbin:/bin:/usr/games:/usr/local/games
PS1=[\u:\w]$ 
PWD=~/flatpak
QT_ACCESSIBILITY=1
QT_LINUX_ACCESSIBILITY_ALWAYS_ON=1
QT_QPA_PLATFORMTHEME=qgnomeplatform
QT_STYLE_OVERRIDE=gtk
SESSION_MANAGER=local/DSS-Mint:@/tmp/.ICE-unix/2014,unix/DSS-
Mint:/tmp/.ICE-unix/2014
SHELL=/bin/bash
SHLVL=1
SSH_AGENT_PID=2125
SSH_AUTH_SOCK=/run/user/1000/keyring/ssh
TERM=xterm-256color
USER=me
_=/usr/bin/env
VTE_VERSION=4205
WINDOWID=102760454
XAUTHORITY=~/.Xauthority
XDG_CONFIG_DIRS=/etc/xdg/xdg-cinnamon:/etc/xdg
XDG_CURRENT_DESKTOP=X-Cinnamon
XDG_DATA_DIRS=~/.local/share/flatpak/exports/share:/var/lib/flatpak/exp
orts/share/:/usr/share/cinnamon:/usr/share/gnome:~/.local/share/flatpak
/exports/share:/var/lib/flatpak/exports/share:/usr/local/share:/usr/sha
re
XDG_GREETER_DATA_DIR=/var/lib/lightdm-data/me
XDG_RUNTIME_DIR=/run/user/1000
XDG_SEAT_PATH=/org/freedesktop/DisplayManager/Seat0
XDG_SEAT=seat0
XDG_SESSION_DESKTOP=cinnamon
XDG_SESSION_ID=c2
XDG_SESSION_PATH=/org/freedesktop/DisplayManager/Session0
XDG_SESSION_TYPE=x11
XDG_VTNR=7