estevaoem It's the default modem configuration, no VLANs in place. Other devices access the server from browsers using the same wifi access point. Not connected as a guest. Why do you think that is not related to GrapheneOS? Asking since it is the only device that isn't reaching the servers in local network
I've mentioned that it most likely is not related to GrapheneOS, it could be though. But i for example also have a bunch of selfhosted services and have no issues, combined with the fact this is the only report regarding an issue like this, made me conclude it most likely isn't related to GOS.
Did u try the suggestion of @0xsigsev by using https://, as far as i remember nextcloud automatically implements https with a self signed certificate. Did u try just for testing with a gecko based browser, for examole firefox? In my recent experience it seems firefox is less strict sometimes. (I've had a service (materialious) over https remote proxying another service accidentaly over http (invidious), and chrome refused to serve http content from a remote source requested by a https domain. Firefox on the other hand did't comolain and allowed mixed content.