Solution: [Bug]: 413 Request Entity Too large (again!) 路 Issue #1830 路 nextcloud/docker 路 GitHub
Another interesting point is that if you access the server externally (from another router/modem), you can upload files >1GiB. Only locally (WLAN/LAN) you have the limitation of 1GiB (but also only via DAV).
Does anyone have any idea why this is the case?