I have tried journalctl -b -o short-monotonic to see what the system is spending time doing while it boots. There are 3 sections (pasted below) where there seems to be an inordinate amount of time going, but i'm not clear what these services actually do and why they might be taking a long time:
Section 1:
[ 11.793005] ASUS-X551CA systemd[1]: Starting udev Kernel Device Manager...
[ 11.827158] ASUS-X551CA systemd-journald[289]: Time spent on flushing to /var/log/journal/566f5db5a1c44e7e82177afc4065ba38 is 106.109ms for 974 entri>
[ 11.827158] ASUS-X551CA systemd-journald[289]: System Journal (/var/log/journal/566f5db5a1c44e7e82177afc4065ba38) is 184.0M, max 1.8G, 1.6G free.
[ 12.009226] ASUS-X551CA systemd[1]: Finished Flush Journal to Persistent Storage.
[ 12.524403] ASUS-X551CA systemd[1]: Started udev Kernel Device Manager.
[ 12.528392] ASUS-X551CA systemd[1]: Starting Show Plymouth Boot Screen...
[ 12.577720] ASUS-X551CA systemd[1]: plymouth-start.service: Succeeded.
[ 12.578114] ASUS-X551CA systemd[1]: Started Show Plymouth Boot Screen.
[ 12.578278] ASUS-X551CA systemd[1]: Condition check resulted in Dispatch Password Requests to Console Directory Watch being skipped.
[ 12.578596] ASUS-X551CA systemd[1]: Started Forward Password Requests to Plymouth Directory Watch.
[ 12.578790] ASUS-X551CA systemd[1]: Reached target Local Encrypted Volumes.
[ 85.123551] ASUS-X551CA kernel: snd_hda_intel 0000:00:1b.0: bound 0000:00:02.0 (ops i915_audio_component_bind_ops [i915])
[ 85.147140] ASUS-X551CA kernel: snd_hda_codec_realtek hdaudioC0D0: autoconfig for ALC270: line_outs=1 (0x14/0x0/0x0/0x0/0x0) type:speaker
[ 85.147143] ASUS-X551CA kernel: snd_hda_codec_realtek hdaudioC0D0: speaker_outs=0 (0x0/0x0/0x0/0x0/0x0)
[ 85.147145] ASUS-X551CA kernel: snd_hda_codec_realtek hdaudioC0D0: hp_outs=1 (0x21/0x0/0x0/0x0/0x0)
[ 85.147146] ASUS-X551CA kernel: snd_hda_codec_realtek hdaudioC0D0: mono: mono_out=0x0
[ 85.147148] ASUS-X551CA kernel: snd_hda_codec_realtek hdaudioC0D0: inputs:
[ 85.147149] ASUS-X551CA kernel: snd_hda_codec_realtek hdaudioC0D0: Mic=0x19
Section 2:
[ 238.012714] ASUS-X551CA systemd[1]: NetworkManager-dispatcher.service: Succeeded.
[ 241.567551] ASUS-X551CA PackageKit[1012]: refresh-cache transaction /54_dadccebd from uid 1000 finished with success after 5530ms
[ 251.009934] ASUS-X551CA geoclue[1011]: Service not used for 60 seconds. Shutting down..
[ 251.017561] ASUS-X551CA systemd[1]: geoclue.service: Succeeded.
[ 252.968858] ASUS-X551CA systemd[557]: Started Application launched by gnome-session-binary.
[ 268.477873] ASUS-X551CA dbus-daemon[575]: [session uid=1000 pid=575] Failed to activate service 'org.freedesktop.Tracker1': timed out (service_start_>
[ 268.479307] ASUS-X551CA tracker-miner-f[1748]: Could not remove files in volumes: GDBus.Error:org.freedesktop.DBus.Error.TimedOut: Failed to activate>
[ 268.480201] ASUS-X551CA tracker-miner-f[1748]: Could not remove files in volumes: GDBus.Error:org.freedesktop.DBus.Error.TimedOut: Failed to activate>
[ 268.480509] ASUS-X551CA tracker-miner-f[1748]: Could not remove files in volumes: GDBus.Error:org.freedesktop.DBus.Error.TimedOut: Failed to activate>
[ 268.480770] ASUS-X551CA tracker-miner-f[1748]: (Sparql buffer) Error in array-update: GDBus.Error:org.freedesktop.DBus.Error.TimedOut: Failed to ac>
[ 268.481049] ASUS-X551CA tracker-miner-f[1748]: Could not execute sparql: GDBus.Error:org.freedesktop.DBus.Error.TimedOut: Failed to activate service >
[ 268.481327] ASUS-X551CA tracker-miner-f[1748]: Could not execute sparql: GDBus.Error:org.freedesktop.DBus.Error.TimedOut: Failed to activate service >
[ 268.481575] ASUS-X551CA tracker-miner-f[1748]: Could not execute sparql: GDBus.Error:org.freedesktop.DBus.Error.TimedOut: Failed to activate service >
[ 313.005788] ASUS-X551CA systemd[557]: Started Application launched by gnome-session-binary.
[ 313.685655] ASUS-X551CA rtkit-daemon[578]: Supervising 5 threads of 3 processes of 1 users.
[ 313.693549] ASUS-X551CA rtkit-daemon[578]: Supervising 5 threads of 3 processes of 1 users.
[ 318.512409] ASUS-X551CA rtkit-daemon[578]: Supervising 5 threads of 3 processes of 1 users.
[ 318.513256] ASUS-X551CA rtkit-daemon[578]: Supervising 5 threads of 3 processes of 1 users.
[ 320.473859] ASUS-X551CA rtkit-daemon[578]: Supervising 5 threads of 3 processes of 1 users.
Section 3:
[ 432.960854] ASUS-X551CA systemd[557]: gnome-launched-org.gnome.DejaDup.Monitor.desktop-3700.scope: Succeeded.
[ 546.004800] ASUS-X551CA PackageKit[1012]: daemon quit
[ 546.018959] ASUS-X551CA systemd[1]: packagekit.service: Succeeded.
[ 590.198869] ASUS-X551CA wpa_supplicant[441]: wlp2s0: WPA: Group rekeying completed with c0:ff:d4:4a:05:c0 [GTK=CCMP]
[ 593.368601] ASUS-X551CA wpa_supplicant[441]: wlp2s0: WPA: Group rekeying completed with c0:ff:d4:4a:05:c0 [GTK=CCMP]
[ 612.926064] ASUS-X551CA wpa_supplicant[441]: wlp2s0: CTRL-EVENT-BEACON-LOSS
[ 632.121843] ASUS-X551CA wpa_supplicant[441]: wlp2s0: WPA: Group rekeying completed with c0:ff:d4:4a:05:c0 [GTK=CCMP]
[ 635.859950] ASUS-X551CA wpa_supplicant[441]: wlp2s0: WPA: Group rekeying completed with c0:ff:d4:4a:05:c0 [GTK=CCMP]
[ 847.001060] ASUS-X551CA NetworkManager[402]: [1625814899.8336] manager: NetworkManager state is now CONNECTED_SITE
[ 847.013238] ASUS-X551CA dbus-daemon[401]: [system] Activating via systemd: service name='org.freedesktop.nm_dispatcher' unit='dbus-org.freedesktop.nm>
[ 847.018079] ASUS-X551CA systemd[1]: Starting Network Manager Script Dispatcher Service...
[ 847.029925] ASUS-X551CA dbus-daemon[401]: [system] Successfully activated service 'org.freedesktop.nm_dispatcher'
[ 847.030336] ASUS-X551CA systemd[1]: Started Network Manager Script Dispatcher Service.
[ 847.422039] ASUS-X551CA NetworkManager[402]: [1625814900.2542] manager: NetworkManager state is now CONNECTED_GLOBAL
[ 858.014964] ASUS-X551CA systemd[1]: NetworkManager-dispatcher.service: Succeeded.
[ 915.868559] ASUS-X551CA systemd[1]: Starting Cleanup of Temporary Directories...
[ 916.094099] ASUS-X551CA systemd[1]: systemd-tmpfiles-clean.service: Succeeded.
[ 916.095091] ASUS-X551CA systemd[1]: Finished Cleanup of Temporary Directories.
[ 968.214403] ASUS-X551CA CRON[3845]: pam_unix(cron:session): session opened for user root by (uid=0)
[ 968.219314] ASUS-X551CA CRON[3846]: (root) CMD ( cd / && run-parts --report /etc/cron.hourly)
[ 968.221148] ASUS-X551CA CRON[3845]: pam_unix(cron:session): session closed for user root
[ 1020.929963] ASUS-X551CA dbus-daemon[575]: [session uid=1000 pid=575] Activating service name='org.gnome.gedit' requested by ':1.57' (uid=1000 pid=939>
[ 1020.974242] ASUS-X551CA dbus-daemon[575]: [session uid=1000 pid=575] Successfully activated service 'org.gnome.gedit'