So after having issues with caching my front page with redis-full-page-caching option -wpredis (otherwise its really great), I went on and setup the https://github.com/SatelliteWP/rocket-nginx. Just go by the setup description on the website and then change your Nginx site configurations as follow:
sudo nano /etc/nginx/sites-available/yourwebsite.com
Having had the wpredis setup config I changed the include part as following:
(uncomment the redis configuration or what ever other caching configuration you setup your initial website e.g. include common/wprocket-php73.conf)
# include common/redis-php73.conf;
#add the php7x.conf instead, please use the right php version in my case php73 and add the rocket-nginx/default.conf
Thats it, works like it should so far and no more Error 405. Maybe you should consider using the https://github.com/SatelliteWP/rocket-nginx for WP-Rocket setup in Wordops for the future.