Nextcloud AIO federated collabora share seems to generate xframe error

Hi,
I have two (rootless, by two different UNIX users) nextcloud aio instances, namely https://cloud.dom1.tld and https://cloud.dom2.tld. The collabora server option is enabled in the two servers - and they work, meaning that if you have a file on one of the two clouds, it opens and can be edited.

Problems arise when a folder, from https://cloud.dom1.tld is shared to https://cloud.dom2.tld through a federated share. Both servers trust each other, so the shared folder is indeed visible to https://cloud.dom2.tld user. Files can be downloaded, reshared, edited, deleted, etc. The command php occ config:app:set richdocuments federation_use_trusted_domains --value="yes" have been executed on both servers (eg, docker instances of nextcloud-aio-nextcloud). And when you try to open a file from the shared folder through collabora, the error “Website will not allow Firefox to display the page if another site has embedded it | Mozilla Support” is thrown.

How to solve that ?
Thanks !