wouldn’t put it past Google to hard code 8.8.8.8 and 8.8.4.4 using DoH in their browser….
Only option is to de-google your browsing experience. Firefox has its own problems, but it’s the only “major” browser left that isn’t based on the Chromium code base. You can switch to IceCat or ZenBrowser, which are based on Firefox too.
Running a pihole is also possible on a Mikrotik router, as it’s possible to get Docker running under RouterOS. But if you’re using Mikrotik you probably already have a NAS or other host in your network that can run containers, too. 🙂