Comment by jasomill

Magic Trackpad 2 and (Mac) Magic Keyboards appear as USB HID devices when connected to a computer via Lightning-to-USB (-A or -C) cable.

One annoyance is that macOS automatically Bluetooth pairs with these devices when connected via USB, overwriting any existing pairing, but this shouldn't matter for purely wired scenarios.

For switching Bluetooth devices more generally, observe that most Bluetooth controllers are USB devices; with a bit of effort — mostly just copy/pasting the device pairing keys across all connected hosts — they can be switched just like any other USB peripheral (YMMV with "intelligent" USB KVM switches that virtualize USB HID device connections).

IME the connection delay is a couple seconds longer than switching wired USB HID devices directly, but entirely reasonable for typical KVM use cases.

Note here that "most Bluetooth controllers are USB devices" even extends to internal Wi-Fi/Bluetooth combo cards, which are commonly M.2 key A or E (= PCIe + USB 2.0 + …), or M.2 key A or E preinstalled on a mostly passive PCIe adapter, with a separate cable connection to a USB port or motherboard USB header used exclusively for Bluetooth.

This turns out to be a surprisingly useful implementation detail: on one of my work desktops, I'm currently virtual USB-switching the Bluetooth controller on an Intel BE200 PCIe card between a Linux host and a Windows VM running on that host, while keeping Wi-Fi connected to the host.

I have a matching hot key set up in each OS to attach/detach the Bluetooth controller from the VM and simultaneously DDC switch the monitor input between the host (iGPU) and guest (PCIe dGPU passthrough), and it works great.

Coincidentally, the Bluetooth devices I'm using in this configuration are a Magic Trackpad 2, a Magic Keyboard, and a Magic Mouse (the mouse was the motivation for using Bluetooth over USB in the first place, as, unlike the other Apple input devices, it's physically impossible to use when connected via USB).