Collabora stopped working after upgrade from NC20.0.14 to NC21.0.8

I have a working NC20.0.14 (nginx, php7.3 Ubuntu 18.04) with Collabora working OK. After upgrading to NC21.0.8 I cannot open or create documents. I just get a blank page. I see no errors in the NC installation or the NC log.
I have tried to remove and reinstall the Collabora Online app (latest) and also remove and reinstall the collabora/code docker. The Collabora Online server is reachable.
I have tried this many times in two servers. Because of this I cannot update my production server.
What next?

The following is my amateurish solution. Some more cunning may have to revise it. But I can now create and edit documents with Collabora in NC21.0.8

I changed the Collabora Online part in the file /etc/nginx/conf.d/nextcloud.conf

The old version was

Start Collabora Online

location ^~ /loleaflet {
proxy_pass https://localhost:9980;
proxy_set_header Host $http_host;
}
location ^~ /hosting/discovery {
proxy_pass https://localhost:9980;
proxy_set_header Host $http_host;
}
location ^~ /lool {
proxy_pass https://localhost:9980;
proxy_set_header Host $http_host;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection “upgrade”;
}
location ^~ /hosting/capabilities {
proxy_pass https://localhost:9980;
proxy_set_header Host $http_host;
}

End Collabora Online

I just copied the proposed passage from this site which is intended for NC23 - but it seems to work.