My oldest “security camera” of this type has been online 24/7 since June 2019 and permanently connected to a charger of the smallest type I could find at that time. The battery still holds a charge when I take the phone down for cleaning. Not sure how old the phone itself is (a small Kyocera), probably a 2014 or 2015 model. So, for my requirements, I’d say, it’s reasonably reliable.
OTOH, you may be right, and they don’t make them like they used to in the olden days, haha.