Heroku's free tier has been incapable of running a 24/7-accessible webserver for many years, nearly a decade[0].
At this point, if anyone is reliant on it, it's almost impressive that they've managed to get by for so long without either paying Heroku or bouncing off to another service.
[0] if you give them a verified credit card, you get a few additional free hours per month, just barely enough to run a single webserver full-time on one dyno. At best, the free tier offering is... incredibly limited.