Ok, I have scoured the forums and have found similar topics in regards to this situation and router but it seems that before a solution is ever found, that topic/thread gets automatically closed. I am attempting to find an actual solution and keep this thread active until a solution is found.
Here's the current setup: I have a Raspberry Pi 4 B 8GB with PiHole running on it (I know, overkill but this is what I had on-hand) directly connected to my Google Fiber router (with a 2.5Gbps plan and there doesn't seem to be a lot of other router options that can properly handle that amount of throughput).
My PC's, TV, etc., for the most part, seem to be working just fine. About 96% of all ads are blocked on ad-blocking test sites (like: Test Ad Block - Toolz) Except... Our android phones are NOT blocking ads when connected to the Google Fiber Router. We have disabled Private DNS on the android devices and have even tried setting static IP's and manually setting the IP address of the PiHole in the android phone but to no avail.
I believe (based on other, similar topics) that the problem stems from this routers inability to disable or even edit IPV6. It doesn't even show any information at all in regards to IPV6 but I know it's being used because when I disable it on Wi-Fi-connected PC's, I get ads blocked. Enable it and ads come through. And unfortunately we are unable to disable IPV6 on our android devices since AT&T locks that. It could be something else but I believe this is the issue as everything on IPV4 works perfectly and blocks all the ads.
It may be worth noting that this is only happening on Wifi and not ethernet/lan-connected devices.
I have also kind of confirmed this theory by plugging in another router (ASUS GT-AXE11000 which has IPV6 disabled) into the network, connected to that router on the Android devices and all ads are blocked. I would just go this route but for some reason, when connected to this router, the upload speeds are just fine (hovering at around 600-800Mbps) but the download speeds are almost nonexistent at a mere 5-10Mbps... I have no idea why. It was working fine on an XFinity/Comcast network but has extremely slow download speeds when connected to this Google Fiber router (connected with a short CAT8 cable but I also tried Cat6 and Cat7 just to see - same result).
Anyway, what I am really trying to find out is if anyone has been able to resolve this issue with the Google Fiber router (which btw, has the most limited user control I've ever seen on a router). Or can it be done through some PiHole settings? I don't think that it can be done through the PiHole but then, I am very new to this.
If the only alternative is to replace the Google Fiber router (which I believe uses an SPF+ connection to the modem), what is the best option that can handle up to 5Gbps (sometimes, during heavy workloads, we bump our service up to 5Gbps... it's awesome. but I haven't been able to find another, 3rd-party router that supports those speeds).
Any advice or solution to this problem would be greatly appreciated. Currently our Android phones get no ads blocked and it's very annoying to say the least.