Thank you @Mohammed90 .
I changed the whole fcgi Block to the line
proxy / localhost:8080
you provided. Now I am not getting a bad gateway error anymore but a 404 Not Found Error from nginx.
The Logs show the following:
# cat /var/log/nextcloud_errors.log
2020/01/31 12:40:21 [ERROR 499 /index.php/favicon.ico] context canceled
2020/01/31 12:40:57 [ERROR 499 /index.php/favicon.ico] context canceled
2020/01/31 12:41:02 [ERROR 499 /index.php/favicon.ico] context canceled
2020/01/31 12:41:15 [ERROR 499 /index.php/favicon.ico] context canceled
2020/01/31 12:46:46 [ERROR 499 /index.php/favicon.ico] context canceled
# cat /var/log/nextcloud_access.log
2020/01/31 12:39:48 87.122.250.47 - - [31/Jan/2020:12:39:48 +0100] "GET / HTTP/2.0" 404 162
2020/01/31 12:39:48 87.122.250.47 - - [31/Jan/2020:12:39:48 +0100] "GET /favicon.ico HTTP/2.0" 404 162
2020/01/31 12:40:21 87.122.250.47 - - [31/Jan/2020:12:40:21 +0100] "GET / HTTP/2.0" 404 162
2020/01/31 12:40:21 87.122.250.47 - - [31/Jan/2020:12:40:21 +0100] "GET /favicon.ico HTTP/2.0" 499 5
2020/01/31 12:40:57 87.122.250.47 - - [31/Jan/2020:12:40:57 +0100] "GET / HTTP/2.0" 404 162
2020/01/31 12:40:57 87.122.250.47 - - [31/Jan/2020:12:40:57 +0100] "GET /favicon.ico HTTP/2.0" 499 5
2020/01/31 12:41:02 87.122.250.47 - - [31/Jan/2020:12:41:02 +0100] "GET / HTTP/2.0" 404 162
2020/01/31 12:41:02 87.122.250.47 - - [31/Jan/2020:12:41:02 +0100] "GET /favicon.ico HTTP/2.0" 499 5
2020/01/31 12:41:15 87.122.250.47 - - [31/Jan/2020:12:41:15 +0100] "GET / HTTP/2.0" 404 162
2020/01/31 12:41:15 87.122.250.47 - - [31/Jan/2020:12:41:15 +0100] "GET /favicon.ico HTTP/2.0" 499 5
2020/01/31 12:43:01 87.122.250.47 - - [31/Jan/2020:12:43:01 +0100] "GET / HTTP/2.0" 302 0
2020/01/31 12:46:46 87.122.250.47 - - [31/Jan/2020:12:46:46 +0100] "GET / HTTP/2.0" 404 162
2020/01/31 12:46:46 87.122.250.47 - - [31/Jan/2020:12:46:46 +0100] "GET /favicon.ico HTTP/2.0" 499 5
I think we are getting closer to resolving the issue. I think it’s not handling the root folder /var/www/nextcloud/ propperly?!
Thank you again for your kind help. Wish all of you a nice weekend! 