Home Assistant Android App - not working correctly with mobile data

Hi,
I wonder why when I use mobile data, the home assistant does not work without providing private DNS (1.1.1.1).
If I connect to another network, it works without any problems (without private dns).

My connection is the domain my-domain.xyz → cloudflare → HA (full secured).
After entering the address in the Chrome browser on mobile data, the HA website is displayed but after logging in, the home page is not displayed.

When I enter private dns 1.1.1.1 - everything works fine.
But unfortunately for other VPN connections - TailScale, I have to disable private dns.

Once upon a time, everything worked fine with a different (national) domain.
Do I need to set anything additional for the .xyz domain?

in order to fix the app you need to make sure everything works in a browser. Most likely something is being blocked somewhere in your setup, make sure everything under the HA domain is whitelisted to avoid blocking things like API and other features

In Firefox
Without private DNS:
Websites prove their identity via certificates. Firefox does not trust https://my-domain.xyz/ because its certificate issuer is unknown, the certificate is self-signed, or the server is not sending the correct intermediate certificate.

With private DNS (1.1.1.1):
the page opens with a padlock and information - Connection is secure.

Could it be that the mobile Internet provider is blocking it in some way? Or is it something to do with the cloudflare settings?

Could it be your local CA that can not be reached?