I use Signal Desktop all the time on my Librem 5 that I use as my daily driver.
I installed is as a flatpak using these instructions.
Note: this is the desktop version, so you still need a another device to be your primary Signal device to connect with. I have still an Android phone with Signal installed for this purpose.
There are a few issues with the Signal Desktop flatpak:
- Keyboard stops working after attaching media/image. See this issue.
- Difficult to slide the contacts side bar narrow (I did this by attaching the L5 to a monitor and mouse).
- Signal Desktop might be energy hungry (not sure if this is still the case).
- Phosh does not show the Signal Desktop icon correctly in application overview. See this issue.
Some more info on the Signal forums:
Signal is ranked number three in fund your app. I donated as well.