A powerful WOL (Wake On Lan) application.
You can launch your Mac/PC from iOS.
(Your computer must support WOL and be properly configured.)
You can also use ping to check the startup.

A little network knowledge is required to use this app.
The OS, BIOS, router, and this app must be configured correctly for it to work.

Siri Shortcuts are also supported.
You can use Siri to launch your computer by adding an action from the Shortcut app.