Screenshot of my Tiny Tiny RSS install on May 7th 2024 after a long struggle with 502 errors.
I had a hard time when trying to update my Tiny Tiny RSS instance running as Docker container behind Nginx as reverse proxy. I experienced a lot of nasty 502 errors because the container did not return proper data to Nginx. I fixed it in the following manner:

First I deleted all the containers and images. I did it with
docker rm -vf $(docker ps -aq) docker rmi -f $(docker images -aq) docker system prune -af
Attention! This deletes all Docker images! Even those not related to Tiny Tiny RSS. No problem in my case. It only keeps the persistent volumes. If you want to keep other images you have to remove the Tiny Tiny RSS ones separately.

The second issue is simple and not really one for me. The Tiny Tiny RSS docs still call Docker Compose with a hyphen: $ docker-compose version. This is not valid for up-to-date installs where the hyphen has to be omitted: $ docker compose version.

The third and biggest issue is that the Git Tiny Tiny RSS repository for Docker Compose does not exist anymore. The files have to to be pulled from the master branch of the main repository https://git.tt-rss.org/fox/tt-rss.git/. The docker-compose.yml has to be changed afterwards since the one in the repository is for development purposes only. The PostgreSQL database is located in a persistent volume. It is not possible to install a newer PostgreSQL version over it. Therefore you have to edit the docker-compose.yml and change the database image image: postgres:15-alpine to image: postgres:12-alpine. And then the data in the PostgreSQL volume were owned by a user named 70. Change it to root.

Now my Tiny Tiny RSS runs again as expected.