Collabora has an option in loolwsd.xml telling it to be behind a proxy and it’s ok to receive the incomming trafic http:
Collabora need to be told with these configuration, if you use SSL and/or proxy. The above link is from our packages, which assumes https used by browser, but terminated before it reaches Collabora by a proxy.
These are all solvable problems, but - sorry to say - I don’t the time to solve them with mile long threads here in the forum.
Ralf