DoTLS and DoHTTPS can be intercepted on your own devices by adding a privately generated certificate to your root store and MITMing the traffic. By design this is the only way to filter this traffic based on content.
Regardless name resolution based ad blocking is relatively futile against even naive workarounds. For instance what is to stop someone from using a custom DoHTTPS format on any webpage to resolve the name directly in browser? What's to prevent them from obfuscating it in a way your MITM couldn't realistically detect?
In the end ad blocking is best done directly on the client through something like uBlock Origin. Not only does this allow you to create a network request block list (now with the added capability of reading/filtering on the whole URI) but it also allows for style based blocks where the ad content could even be blocked if it comes from the same server and resources serving the actual page.
Of course, a pihole will not be able to block someone who goes to the length of developing and using a custom DNS-over-TLS or DNS-over-HTTPS webpage.
Similarly uBlock origin is not available for anything else except browsers. There is nothing preventing native apps from using or pinning different nameservers. On a scale of hardness, using or pinning a specific DNS server is easy and is known to be used in wild. Custom DoT or DoH is still rare but I am aware that there will be a time when a significant chunk of internet will use it.
Name-resolution based ad-blocking is not futile yet. My pihole has alone blocked 5k+ queries in the past 24h.
Regardless name resolution based ad blocking is relatively futile against even naive workarounds. For instance what is to stop someone from using a custom DoHTTPS format on any webpage to resolve the name directly in browser? What's to prevent them from obfuscating it in a way your MITM couldn't realistically detect?
In the end ad blocking is best done directly on the client through something like uBlock Origin. Not only does this allow you to create a network request block list (now with the added capability of reading/filtering on the whole URI) but it also allows for style based blocks where the ad content could even be blocked if it comes from the same server and resources serving the actual page.