I am using BitDefender's VPN product which offers an ad blocking function and split tunneling
If I turn split tunneling on and allow an app to bypass the VPN, will it also bypass the ad block function or will the adverts still be blocked?
According to the documentation, the ad blocker is a part of the VPN. Traffic going outside of the VPN would not benefit from the VPN's features, like ad blocker and anti-tracker.
The reason why the ad blocker requires the VPN is that BitDefender blocks IPs at the DNS level (which is how you can allow certain sites) which is a network-level intervention.