The most recent edition of "Handbook of Software Engineering Methods" by Lara Letaw is available at https://open.oregonstate.education/setextbook/
Compared to the one here, the latest version more accessible, is in web format, and has been updated throughout.
I plan to continue using this repo for issue tracking.
You can still download the old, PDF version at https://github.com/setextbook/setextbook/raw/main/Handbook_of_Software_Engineering_Methods.pdf