Synology-OpenVPN-adguard dns

I have a Synology NAS at home, where I have installed OpenVPN. When I am on other WiFi networks, such as at work, I connect to the local WiFi and activate OpenVPN on my device. This way, all my traffic is routed through an encrypted tunnel to my home, bypassing any network restrictions or filters at work. Additionally, websites with geographic or network restrictions are also accessible since my internet traffic exits through my home router.

Besides the VPN, I also use Private DNS (dns.adguard.com) on my phone for ad filtering. Here’s the issue:

If I don’t specify a DNS in OpenVPN, everything works fine. I can see local devices in my home network and access the internet.

If I set a specified DNS (dns.adguard.com) in OpenVPN, I can only access local devices (e.g., my router or Synology via local IP), but I lose internet access.

If I disable Private DNS on my phone, the VPN works properly, allowing both local and internet access, but ad filtering is disabled.

The strange thing is that with the exact same setup a few months ago, there was no issue. After moving to a new place and changing my internet connection/router, I’m not sure what has changed.