this does not work. all addresses used to interact between the systems must be the same as the client uses. You route the traffic internally (using internal IPs) but there is no way to use internal DNS names…
UPDATE: there is a way avoid external communication. The technique is well-known splitbraindns but for Docker it must be done “internally” so Docker routes requests to public DNS directly to the reverseproxy. see Probably DNS help with NC Docker + Collabora + Wireguard tunnel - #5 by wwe for details.