Aha! Thanks, I didn’t know PureOS was based on buster (testing). I’m coming from various versions of Ubuntu, like Xubuntu and Lubuntu, so I’m now getting used to the GNOME environment and educating myself about Debian and its other variants besides Ubuntu.
I’ve been using GnuCash for 10 years, so I needed it right away if I wanted to make the Librem 15 my main machine. Since it’s such a NICE machine, I persevered. Luckily, flatpak came to the rescue and GnuCash was already on flathub.org. Between flatpack and snap I’ve installed the few things I need that aren’t in the PureOS repo.
By the way, the sluggishness with the Backspace and Del keys in GNOME apps was apparently caused by logging in while choosing GNOME on Xorg instead of GNOME from the gear menu 
.