Update: some users were unable to load the site (assets and files). We’ve found that the contabostorage.com domain was present in some blocklists as a phishing site. The solution was simple:
setup a subdomain files.mydomain.com like described here Can I Setup a Custom Domain for My Object Storage? : Contabo
Updated DISCOURSE_S3_CDN_URL: https://files.mydomain.com in app.yml
Then
cd /var/discourse
sudo ./launcher rebuild app
and to complete the job
./launcher enter app
rake posts:rebake
Now all assets and uploads load from https://files.mydomain.com/pathtofile/file.ext
Done