How to lose time while reinstalling its Mastodon server and trying to understand why images don't display.
Set "SWIFT_ENABLED=True" instead of "SWIFT_ENABLED=true" in the configuration file.
Don't see it because in your YAML Ansible configuration file you have put "SWIFT_ENABLED: true".
Set "SWIFT_AUTH_URL=https://auth.cloud.ovh.net/v3.0" instead of "SWIFT_AUTH_URL=https://auth.cloud.ovh.net" because before it was "SWIFT_AUTH_URL=https://auth.cloud.ovh.net/v2.0".
Nevermind. It works again!