If you stream from a home PC to your iPhone with Moonlight or Steam Link, the PC has to be awake first. Moonlight's own wake often does nothing on an iPhone, or works one day and not the next.
I make Radien, an iPhone app with Wake on LAN, so I'm not neutral here. Still, the setup below helps whatever wake app you use, and my app comes only at the end.
Why it fails on an iPhone
Moonlight sends the Magic Packet to 255.255.255.255, and iOS refuses that address unless the app holds Apple's multicast networking entitlement. Its other packet goes to the PC's own address, and that gets through only while the iPhone still remembers the sleeping PC, about 20 minutes. That is the "worked yesterday, not today" pattern.
Set the PC up once (Windows)
In the BIOS or UEFI, turn on Wake on LAN. It can be called Power On by PCI-E.
In Device Manager, open the network card. In Power Management, turn on "Allow this device to wake the computer". In Advanced, turn on Wake on Magic Packet.
Turn off Fast startup: Control Panel, Power Options, Choose what the power buttons do.
Use a cable. A wake over Wi-Fi rarely works.
Give the PC a fixed address on your router (a DHCP reservation).
Let it sleep rather than shut down. After a shutdown, Steam Remote Play works only once someone has signed in to Windows.
To wake it from a full shutdown too, turn off ErP or EuP in the BIOS (on some boards it is called Deep Sleep), and don't plug it into a power strip you switch off: the network card needs power to listen. The MAC address is the Physical Address that ipconfig /all shows for the wired card.
Away from home
The packet needs a way in: your own VPN into the home network (WireGuard or Tailscale on the router, or on a Pi or a NAS that stays on), or a forwarded UDP port on the router, which cannot work behind CGNAT. A VPN that runs only on the gaming PC cannot help: it sleeps with the PC. Either way, a packet to the PC's own address gets through only while the device at home still remembers the sleeping PC; a static ARP entry for the PC there fixes that.
The app part
Radien holds that entitlement. It sends the Magic Packet, then watches the PC, so it tells you whether the PC answered rather than just "sent". Its Wake Device action in Shortcuts returns a result you can check, so one shortcut can wake the PC and, if the result is Answered, open Moonlight or Steam Link. Turn off Show When Run so it runs straight through, and put it on the Action button or your Home Screen.
One computer is free, the Shortcuts action included. Radien Pro, a one-time purchase, also waits for Moonlight's port 47989 or Steam's 27036 (a PC can answer ping before the stream is ready), and sends the packet through your VPN or a forwarded port when you are away.
The full guide, with screenshots of the shortcut: https://radien.arsenkin.name/guides/wake-gaming-pc-moonlight-steam-link
If your PC still won't wake, ask here and I'll try to help, whatever app you use.
