@chrisphl, thank you for your reply!
There are many with semi-bricked GS290 who then appear to brick them by using SP flashtool!
I would very much like to see how we could assist some GS290 owners by writing a recovery solution, perhaps with TWRP?
Post script edit.
What follows is a small walkthrough of a suggested method of rescue for GS290.
Although this thread is originally titled “how to root and install ZIP files” the proposed rescue method which follows does not use use or expect root.
The version of TWRP used here is twrp-3.5.0-35-GS290.img
found here
https://build.lolinet.com/file/twrp/GS290/android-10.0/twrp-3.5.0-35-GS290.img