Using laptop keyboard as wireless bluetooth keyboard

On Macs, the application type2phone offers exactly this functionality. As long as this application is active (i.e. not in the background), all keyboard input is sent to a paired iPhone (or in fact, any device that supports input from bluetooth keyboards). No software whatsoever needs to be installed on the target device, since all it sees is a generic bluetooth keyboard. Actually i have been looking for a windows pendant to type2phone, but haven't found one yet.

If a virus/malware/whatever is intercepting keystrokes, then changing the method of connection to the PC is irrelevant. USB, wireless, Bluetooth, PS2, AT, etc, it doesnt matter.

Across can do this. It supports sharing keyboards attached to a Windows or macOS machine to anything that supports Bluetooth, including Windows, macOS, iOS, and Android devices.

I don't have much experience with it. I actually came across both that software and this question today, trying to do something similar myself. I hope it works well for both of us :).

If you use the trial, note the somewhat unorthodox trial limitations, which can appear to be bugs at first glance:

The trial version only works without any limit for 30 minutes after computer starts. After the 30 minutes, mouse works without any limit, but when you input keyboard to a client device with the trial version, you will be unable to input the ‘Q’, ‘W’, ‘E’, ‘I’, ‘O’, ‘P’ keys of a keyboard (the ‘A’, ‘Z’, ‘E’, ‘I’, ‘O’, ‘P’ keys of a French keyboard) to the device. Also, the length of the clipboard text that can be synchronized between devices is limited.