Hi @peter-kehl, thanks for the link and also for opening the GitHub issue, I will definitively keep an eye on it!
EDIT: Resetting Cinnamon to default settings seems to have solved the issue for me! More details on Add/Remove Software seg fault/not showing.
EDIT 2: sadly, it seems that it was only a temporary fix!
After 6 days working as expected, pamac-manager started to segfault again 
I didn’t change anything on my system since then, the only noticeable event was an update of Firefox and Chromium yesterday…