Why can’t I connect Nextcloud to a native Synology NAS Nextcloud server install?

I’ve installed Nextcloud client on Garuda Linux and Nextcloud native server on a Synology DS720+ NAS (outside of Docker). First time I tried to connect the Nextcloud client to my server I get:

Failed to connect to Nextcloud at https://[REDACTED]/nextcloud: The server enforces strict transport security and does not accept untrusted certificates.

I didn’t do anything with my server at this point. At the moment I’ve got this error message from the logs on the server:

HTTP headers
Some headers are not set correctly on your instance – The Strict-Transport-Security HTTP header is not set (should be at least 15552000 seconds). For enhanced security, it is recommended to enable HSTS.

I think I’d like to disable HSTS for now and set it up later but it won’t take no unsecure connections nor unknown certificates at the moment. How do I disable HSTS and carry on unsecured for now until I’ve learned more about the process?

Just to mention as well that I’ve got 2 routers between my computer and the NAS. I have an EE Smart Hub which in turn is connected to a Linksys WRT1900ACS which then is connected to the NAS. I can connect my Android phone successfully by connecting the phone to the Linksys router. No problems there. But the Linux client I have problems with.