Dear Adam,
waiting eager for a update for Thunderbird 68.4.1 (meanwhile I can bearly live without Archive This...) I just (manually) installed archive_this-1.5.0.0-tb.xpi. After changing the shortcuts (Alt-1 to -9 which I used earlier seem not to work any more, so I tried Ctrl-Alt-1-9 and Ctrl-F1-F9) and defining the folders I tried the new shortcuts - but nothing happens.
What's working: Alt-0, Ctrl-Alt-M, Ctrl-Alt-C, Ctrl-Alt-G. Everything else: imply nothing, even after restarting Thunderbird etc. :-(