First look in log files. Use Log File Viewer and open dmesg. I should show the current boot and several previous versions like dmesg.0 or .1 etc. If not shown in default you have to open it from /var/log.
Look for some driver or device that takes a very long time, or repeats & fails.
If you had abnormal shutdowns the e2fsck could still help. Every 40 or 60 boots it runs fsck and if any issues may run it. That can slow booting by several minutes.
Thanks OldFred. I have looked at dmesg logs but cannot figure out much, long and cryptic.
I'll boot from usb and attempt e2fsck on unmounted drive. I'll report back when done.