Time to move on I guess.
Does anyone have good hosting suggestions for a web app that has a 1GB database and a few thousand active users?
I can only afford ~10-20 EUR a month on shared hosting atm.
TL;DR: Too expensive.
(And, additionally, they tend to fuck over customers who paid for their money. "100$ free credit!". "You only need to pay 5$ to activate your free credit!". "Sorry, but because you didn’t use it, we removed your free credit!")
Sounds to me like you can move to a better host that does provide LetsEncrypt and save money on your hosting costs to boot!
9 EUR, 2 cores + 6 GB RAM, 40 GB SSD.
It still baffles me that someone is using shared hosting services and upload their php files via ftp...
I agree that the best option is for shared hosts just to build in support for LetsEncrypt.
Anything I can do other than not using S3?
(I'm probably understanding this wrong, but I'd like to understand why.)
I think it's time for a bit of light monetization.
That's definitely a significant security risk, even if it wasn't being explicitly labeled before now. It sucks for independent website operators like you, but I'd probably blame your hosting for making it difficult to secure your site rather than browser vendors for protecting their users.