Yes, it is possible to run scrcpy from the shell without USB or wireless debugging, but with some limitations:
OTG Mode: You can use scrcpy in OTG (On-The-Go) mode, which allows you to control the device using a physical keyboard, mouse, or gamepad connected via an OTG cable. In this mode, USB debugging is not required. You can run scrcpy with the --no-video --no-audio --keyboard=uhid --mouse=uhid flags to simulate input events without mirroring the screen. The OTG mode is designed for controlling the device directly via HID (Human Interface Device) without ADB or USB debugging enabled.
Control Without Mirroring: If you only need to send input events (like keyboard and mouse) and do not require screen mirroring, OTG mode is the solution. However, this does not provide live screen mirroring.
Note: This feature is especially useful for devices with broken screens, as you can enable USB debugging later via the simulated input.
Would you like the exact command for your specific use case?