Yes, I found that link you cited a day ago and tried it before seeing your post.
Found my file under ~/Library⁩/Containers⁩/com.apple.Safari⁩/⁨Data⁩/Library⁩/⁨Preferences⁩/com.apple.Safari.Extensions.plist.

1. I dragged that file onto SRExport, but a "SRExport quit unexpectedly" error was returned:
   Crashed Thread: 0 Dispatch queue: com.apple.main-thread

Exception Type: EXC_BAD_INSTRUCTION (SIGILL)
Exception Codes: 0x0000000000000001, 0x0000000000000000
Exception Note: EXC_CORPSE_NOTIFY

Termination Signal: Illegal instruction: 4
Termination Reason: Namespace SIGNAL, Code 0x4
Terminating Process: exc handler [7530]

1. went to https://sessions-extension.github.io/Sessions/export.html , downloaded the script and following the instructions attempted to run it. Terminal returned the following error:
   ERROR /Users/danielcarlock/Library/Safari/Databases/safari-extension_yoo.david.sessions-deub45nr9t_0/ is either unreadable or contains no databases.

What should I try next?

Re: lost previous sessions on upgrade

SessionRestore disappeared from Safari for me, possibly when Apple released v13 of Safari?
Last version of SessionRestore.safariextz on my computer was 8/11/2018.
So after reading your support BB, I upgraded to version 1.7 of SessionRestore.
Upon starting it, my previous saved history states are not shown.
Recall that you fixed this for me once before (8/13/2018).
How can I get my previous history to reload?

Yes I do, and restored it to my desktop according the the procedure you prescribed above on 2-28-2017, 02:48 AM. However, only the session https://sweetpproductions.com/support/showthread.php?tid=582 is restored - namely, the page that contains this BB forum.

This is odd because in looking at my old, restored com.apple.Safari.Extensions.plist file, I see seven (7) text blocks beginning with the string data:image/png;base64. Peeking at them with a text editor, I can easily see that they contain the URLs of the sites contained in the old sessions.

Not sure what to do next.

I've used SessionRestore for quite a while now, but was shocked when it disappeared from my Safari installation following my last Mac OS update (to Safari 11.1.2 / MacOS 10.13.6). Reading elsewhere on the SweetP BB's, I found both an updated version of SessionRestore (v9.1) and a utility for recovering previously stored sessions (SRRecover v1.0). However, dropping a com.apple.Safari.Extensions.plist file on SRRecover doesn't create an import file.

Is there a High Sierra compatible version of SRRecover? I really want to restore all of my previously saved sessions! Thanks.