For Windows, it's mostly the same as always even on Windows 11. It's under the IPv4 (or IPv6 as applicable) properties of whichever connection you're using.
The exact way to get to it varies slightly by Windows version, but it's somewhere under the vicinity of Control Panel -> Network and Internet -> Network Connections (this particular example is from Windows 7).
For Android, this also varies slightly by each device manufacturer's own flavor of Android, but it's usually somewhere under the section to do with device connections (Wi-Fi, Bluetooth, etc.) and is called "Private DNS".
You need to give it a hostname (usually a domain name, eg: dns.google for 8.8.8.8 and 8.8.4.4.) rather than an IP address, presumably because it's DNS Over HTTPS? I'm not quite sure why it doesn't take IP addresses.
I was asking specifically for android, should've clarified that. I was fully expecting this exact answer btw.
Switching to DoH or private DNS in Android does not change the default DNS. How do you think you get the IP from the hostname when you enable DoH? 8.8.8.8 is hard coded and there's no way to change it without hacky stuff. Every time you request a record from your configured DoH server, it queries 8.8.8.8 to get the IP of that server hostname. I chose this example specifically because I'm extremely familiar with it, a good example it does make.
Are you still unsure why you can't enter an IP address instead of a hostname? There's literally no user oriented reason for this, the developer had to go out of their way to prevent it. This sort of deliberate restriction is why I call it a kiosk. Why wouldn't they indeed.
And it's not the only one in android, and it hasn't always been there. It was introduced in a later version, early versions of android left the DNS server configurable. Another good one is tethering reporting to your carrier. Look into how that works, it's ridiculous. Why is my device doing things I don't want it to do and preventing me from stopping it? Is this thing mine or not?
I actually don't make use of the Private DNS feature myself, because one time I had it set and it somehow broke connections to everything. Probably some catch 22 nonsense going on, since it wants a hostname but you need DNS to know where the hostname goes.
Also, apologies, some of that beer I had for dinner must still be in me because I forgot another way to set DNS servers on Android, at least partially.
Under whatever connections (Wi-Fi, etc.) is called again, going into all the various Wi-Fi connections I can set a specific DNS server (actually two servers) to use with the connection. Basically kind of like how Windows configures it. Of course, it doesn't apply to the mobile data connection, which is annoying and definitely a mark against Android...
Not to get in the way of a good conspiracy theory, but the reason you can't enter a plain IP is because the H in DoH stands for Https, and there's no way to validate SSL against a bare IP. A false sense of security is worse than a bad one!
The exact way to get to it varies slightly by Windows version, but it's somewhere under the vicinity of Control Panel -> Network and Internet -> Network Connections (this particular example is from Windows 7).
For Android, this also varies slightly by each device manufacturer's own flavor of Android, but it's usually somewhere under the section to do with device connections (Wi-Fi, Bluetooth, etc.) and is called "Private DNS".
You need to give it a hostname (usually a domain name, eg: dns.google for 8.8.8.8 and 8.8.4.4.) rather than an IP address, presumably because it's DNS Over HTTPS? I'm not quite sure why it doesn't take IP addresses.