Unfortunately, self-building an image is way beyond my knowledge/skills.
I tried systemd-analyse blame, here are the first few lines...
41.351s wait-time-sync.service
30.036s kodi-waitonnetwork.service
3.602s dev-mmcblk0p2.device
3.557s dev-mmcblk0p1.device
3.491s dev-loop0.device
2.916s pulseaudio.service
2.612s systemd-hwdb-update.service
2.000s connman-vpn.service
1.927s iwd.service
1.926s dbus.service
1.397s samba-config.service
1.061s systemd-logind.service
Similar to the one you linked to, except the much slower times.
I tried disabling BT, it made no measurable difference.
You said "unplug the USB Gigabit Ethernet adapter", but there's isn't a USB adapter plugged in. The only USB thing plugged in at the moment is a keyboard.