Here's the results of the logs for sddm:
ps -eaf | grep sddm
root 1497 1 0 17:59 ? 00:00:00 /usr/bin/sddm
root 1501 1497 0 17:59 tty1 00:00:00 /usr/libexec/Xorg -nolisten tcp -auth /var/run/sddm/{a1d9270c-38d2-4241-8d36-caf7228d5813} -background none -noreset -displayfd 16 -seat seat0 vt1
root 1640 1497 0 17:59 ? 00:00:00 /usr/libexec/sddm-helper --socket /tmp/sddm-autheb500c3c-e0c2-4f60-a477-8589baccf976 --id 2 --start /usr/bin/sddm-greeter --socket /tmp/sddm-:0-WzNaeg --theme /usr/share/sddm/themes/01-breeze-fedora --user sddm --greeter
sddm 1641 1 0 17:59 ? 00:00:00 /usr/lib/systemd/systemd --user
sddm 1643 1641 0 17:59 ? 00:00:00 (sd-pam)
sddm 1648 1641 0 17:59 ? 00:00:00 /usr/bin/pulseaudio --daemonize=no
sddm 1649 1640 1 17:59 ? 00:00:00 /usr/bin/sddm-greeter --socket /tmp/sddm-:0-WzNaeg --theme /usr/share/sddm/themes/01-breeze-fedora
sddm 1674 1641 0 17:59 ? 00:00:00 /usr/bin/dbus-daemon --session --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
sddm 1700 1648 0 17:59 ? 00:00:00 /usr/libexec/pulse/gconf-helper
sddm 1702 1641 0 17:59 ? 00:00:00 /usr/libexec/gconfd-2
testuser 1789 1740 0 18:00 tty2 00:00:00 grep --color=auto sddm
journalctl -b 0 | grep sddm
Aug 18 17:59:36 testlaptop.test.domail audit[1]: SERVICE_START pid=1 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:init_t:s0 msg='unit=sddm comm="systemd" exe="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=success'
Aug 18 17:59:38 testlaptop.test.domail audit[1640]: USER_AUTH pid=1640 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:xdm_t:s0-s0:c0.c1023 msg='op=PAM:authentication grantors=pam_permit acct="sddm" exe="/usr/libexec/sddm-helper" hostname=? addr=? terminal=? res=success'
Aug 18 17:59:38 testlaptop.test.domail audit[1640]: USER_ACCT pid=1640 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:xdm_t:s0-s0:c0.c1023 msg='op=PAM:accounting grantors=pam_permit acct="sddm" exe="/usr/libexec/sddm-helper" hostname=? addr=? terminal=? res=success'
Aug 18 17:59:38 testlaptop.test.domail audit[1640]: CRED_ACQ pid=1640 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:xdm_t:s0-s0:c0.c1023 msg='op=PAM:setcred grantors=pam_permit acct="sddm" exe="/usr/libexec/sddm-helper" hostname=? addr=? terminal=? res=success'
Aug 18 17:59:38 testlaptop.test.domail sddm-helper[1640]: pam_unix(sddm-greeter:session): session opened for user sddm by (uid=0)
Aug 18 17:59:38 testlaptop.test.domail systemd[1]: Created slice User Slice of sddm.
Aug 18 17:59:38 testlaptop.test.domail systemd-logind[1254]: New session c1 of user sddm.
Aug 18 17:59:38 testlaptop.test.domail systemd[1]: Started Session c1 of user sddm.
Aug 18 17:59:38 testlaptop.test.domail audit[1641]: USER_ACCT pid=1641 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:init_t:s0 msg='op=PAM:accounting grantors=pam_unix,pam_localuser acct="sddm" exe="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=success'
Aug 18 17:59:38 testlaptop.test.domail systemd[1641]: pam_unix(systemd-user:session): session opened for user sddm by (uid=0)
Aug 18 17:59:38 testlaptop.test.domail audit[1641]: USER_START pid=1641 uid=0 auid=995 ses=1 subj=system_u:system_r:init_t:s0 msg='op=PAM:session_open grantors=pam_selinux,pam_selinux,pam_loginuid,pam_keyinit,pam_limits,pam_systemd,pam_unix acct="sddm" exe="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=success'
Aug 18 17:59:38 testlaptop.test.domail audit[1640]: USER_START pid=1640 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:xdm_t:s0-s0:c0.c1023 msg='op=PAM:session_open grantors=pam_unix,pam_systemd acct="sddm" exe="/usr/libexec/sddm-helper" hostname=? addr=? terminal=:0 res=success'
Aug 18 17:59:39 testlaptop.test.domail sddm-greeter[1649]: Loading file:///usr/share/sddm/themes/01-breeze-fedora/Main.qml...
Aug 18 17:59:39 testlaptop.test.domail sddm-greeter[1649]: QObject: Cannot create children for a parent that is in a different thread.
Aug 18 17:59:39 testlaptop.test.domail sddm-greeter[1649]: QObject: Cannot create children for a parent that is in a different thread.
Aug 18 17:59:39 testlaptop.test.domail sddm-greeter[1649]: QObject: Cannot create children for a parent that is in a different thread.
Aug 18 17:59:39 testlaptop.test.domail sddm-greeter[1649]: QObject: Cannot create children for a parent that is in a different thread.
Aug 18 17:59:39 testlaptop.test.domail sddm-greeter[1649]: QObject::installEventFilter(): Cannot filter events for objects in a different thread.
Aug 18 17:59:39 testlaptop.test.domail sddm-greeter[1649]: QObject: Cannot create children for a parent that is in a different thread.
Aug 18 17:59:39 testlaptop.test.domail sddm-greeter[1649]: QObject: Cannot create children for a parent that is in a different thread.
Aug 18 17:59:39 testlaptop.test.domail sddm-greeter[1649]: QObject::installEventFilter(): Cannot filter events for objects in a different thread.
Aug 18 17:59:39 testlaptop.test.domail sddm-greeter[1649]: Cannot watch QRC-like path ":/icons/hicolor/index.theme"
Aug 18 17:59:39 testlaptop.test.domail dbus-daemon[1284]: [system] Activating via systemd: service name='org.freedesktop.UPower' unit='upower.service' requested by ':1.46' (uid=995 pid=1649 comm="/usr/bin/sddm-greeter --socket /tmp/sddm-:0-WzNaeg" label="system_u:system_r:xdm_t:s0-s0:c0.c1023")
Everything appears fine with the nVidia settings app and the System settings once KDE has loaded.
I'll try again with LightDM in a couple hours, my ravening horde is at the babygates!
Thomas