You can simply use the IP address. If your goal is to connect an iPad to a Windows 11 Pro PC using Remote Desktop, you do not need the fully qualified domain name.
On the Windows PC, open Command Prompt and run:
ipconfig
Find the active network adapter and look for the IPv4 Address, for example:
IPv4 Address. . . . . . . . . . : 192.168.1.25
Then, in the Microsoft Windows App on the iPad, create a new PC connection and enter:
192.168.1.25
as the PC name/address.
There are however a few consideration.
The first one is your Windows 11 edition. Windows 11 Pro can act as an incoming Remote Desktop host - Windows 11 Home cannot. Also make sure Remote Desktop is enabled on the Windows 11 Pro PC under Settings > System > Remote Desktop.
The second one is whether the IP address will remain the same. If the PC receives its address through DHCP, your router could eventually assign it a different address. The easiest solution is to create a DHCP reservation for that PC in your router. The PC will then consistently receive the same IP address.
The third one one applies If you're trying to connect to the PC from outside your home or office network, that's different. You should generally use a VPN or another secure remote-access solution rather than exposing RDP directly to the Internet.
If the above response helps answer your question, remember to "Accept Answer" so that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.
hth
Marcin