Hello,
I'm currently running the in-development Trisquel 9.0 and can confirm that
KeepassXC is there...
keepassxc/etiona 2.3.1+dfsg.1-1 amd64
Cross Platform Password Manager
An option to get it on an a Trisquel 8.0 system is to install it using Guix
(an alternative GNU packaging system that several people here on the forum
have installed on Trisquel). Guix currently has keepassxc 2.3.4 available.
If you search for 'Guix' on the forum here there is some discussion about
what it is, and how to set it up.
