Hello again @elias,
thank you for your help already. this is the errorlog from my chromium:
https://website.de/static/bundle-3.0.3.js Failed to load resource: the server responded with a status of 404 (Not Found)
website.de/:1 Uncaught TypeError: window.setup_root is not a function
https://website.de/static/files/f3ee0663271515c7f6aeb4b8f47d5c12.png Failed to load resource: the server responded with a status of 404 (Not Found)
https://website.de/static/files/3d9b3740060310158cf259a1c2c0ddc9.png Failed to load resource: the server responded with a status of 404 (Not Found)
https://website.de/static/files/02100a5664ea1bf9e4990ad37936af4a.png Failed to load resource: the server responded with a status of 404 (Not Found)
https://website.de/static/files/10ee7f4daf66060a2af9c5eef914b4c8.png Failed to load resource: the server responded with a status of 404 (Not Found)It seems, that nginx does not pass the subfolder to mattermost instead of https://website.de/mattermost/ it passes https://website.de/ and then mattermost can not find its files.
I've tested the page also with another browser. I also created a different configuration where nginx listens to website.de:8080 and passes it to mattermost (without any subfolder). This works just fine, but a different port than 443 is not possible with my situation here.
Regards
marove