There are a few ways to bypass pi-hole. Refer to this post to block the majority of them: Do individual devices require configuration with Pihole+Unbound?
There has also been a new pi-hole setting: dns.specialDomains.designatedResolver to prevent clients from upgrading to DoH via the upstream provider. Make sure this is set to true.
Edit: I just want to make clear that these bypasses are not a fault of pi-hole