Hi @Twisty welcome to /e/ land.
Is critical - @OneThumb provided this clue recently: [GSI] Q-GSI --- new version download location. See post 73 - #109 by OneThumb
Please be aware that anything which involves “a backup of your EFS partition” requires careful thought, reading and preparation.
This is the /e/ documentation page
https://doc.e.foundation/how-tos/install-GSI
Bon chance