Customizing GDM3 Themes in Ubuntu 20.04 Focal Fossa

After upgrading to the latest LTS Ubuntu 20.04, I decided to stop using the old standard lightdm-gtk-greeter and give in to using Gnome’s gdm3. But I don’t like Ubuntu’s default styles — in fact, I use a vanilla gnome-session entirely to avoid the purple flash you get on ubuntu-session. After some research, I found you

libsystemd-daemon-dev error when Compiling Transmission on Ubuntu 16.04+

Due to vulnerabilities in Transmission 2.92 and lower, it’s important to upgrade to 2.93+, except the Ubuntu PPA has not yet been updated. Thus, one compiles!

Except, I found that compiling on Ubuntu 16.04 and above, I then could not start the service with systemd.