The same issue on my system, however, the fix of setting "~/.config/bluedevilglobalrc contains a line with my adapters MAC with "_powered=" to true keeps getting reverted every time I open the Bluetooth settings in KDE. 

another 'fix' is after setting the powered option to true make the file read-only so that it doesn't get set to false again

Operating System: Garuda Linux 
KDE Plasma Version: 5.27.5
KDE Frameworks Version: 5.106.0
Qt Version: 5.15.9
Kernel Version: 6.3.6-273-tkg-bmq (64-bit)
Graphics Platform: Wayland
Processors: 12 × AMD Ryzen 5 5600X 6-Core Processor
Memory: 31.3 GiB of RAM
Graphics Processor: AMD Radeon RX 6700 XT

Same issue with me. I noticed the situation that Andres is also using Wayland, and the configuration file ~/.config/bluedevilglobalrc is synchronized with GUI bluetooth settings on X11 session ( It seems on Wayland the configuration could only be read but not written ) . So I guess maybe they just didn't fit settings application properly to write a configuration file?

*** Bug 470736 has been marked as a duplicate of this bug. ***

As far as I can tell it's broken both on X11 and Wayland for me when rebooting.

What's interesting is that it seems to work when rebooting via 'reboot', but not when clicking reboot in Kickoff.

It is supposed to save the state when kded5 quits, see https://invent.kde.org/plasma/bluedevil/-/blob/master/src/kded/bluedevildaemon.cpp#L107

When I manually call "kquitapp5 kded5" it indeed writes the config, but not when rebooting, which might suggest that kded5 is terminated ungracefully on reboot

Still present in
Operating System: Gentoo Linux 2.14
KDE Plasma Version: 5.27.7
KDE Frameworks Version: 5.108.0
Qt Version: 5.15.10
Kernel Version: 6.4.7-cova (64-bit)
Graphics Platform: Wayland

Same here on plasma 5.27 on arch
I do notice that toggling enabled on / off under settings > bluetooth > configure does not change anything in this file.
Where I would expect it if anything. 

Changing it to powered=true in bluedevilglobalrc as described in the opening comment does help.
It generally survives reboots / shutdowns but does get reset at times, possibly upon system updates.

This still occurs on plasma-wayland 6.0.2, kernel 6.8.2. I dont know if this is relevant but I'm getting:
kf.bluezqt: PendingCall Error: "The name is not activatable" in my journal

Manualy editing bluedevilglobalrc still helps it it gets reset.

In my system, there is "<MAC_ADDRESS>_powered=false" under [Adapter] group and my Bluetooth adapter will not power on after logout and in or reboot. If I delete this line everything will be fine.
My system is KDE 6.0/3 Arch Linux.

Same here on KDE 6.0.4 & Arch Linux with 6.8.7 kernel.

This bug happens very randomly, even when no update was excuted. But resetting `~/.config/bluedevilglobalrc` helps.

*** Bug 482783 has been marked as a duplicate of this bug. ***

*** Bug 479868 has been marked as a duplicate of this bug. ***

Git commit d71bfa54089b388a83473599a4dfce6ff06b4be6 by Nate Graham, on behalf of Arctic Lampyrid.
Committed on 25/04/2024 at 17:33.
Pushed by ngraham into branch 'master'.

kded: Fix `launchState` setting not working

Before setting the initial state, we need to wait for the manager to
be operational.

`restoreAdapter()` is scheduled to be called after 1 second when
`adapterAdded` is emitted. Thus after applying `launchState` settings,
`saveState` should be called to avoid restoring to an incorrect state.

Signed-off-by: Arctic Lampyrid <ArcticLampyrid@outlook.com>
FIXED-IN: 6.0.5

M  +24   -0    src/kded/devicemonitor.cpp
M  +4    -0    src/kded/devicemonitor.h

https://invent.kde.org/plasma/bluedevil/-/commit/d71bfa54089b388a83473599a4dfce6ff06b4be6

Git commit 2cc4a2ed3e573df8760b8db6805a5396d89f3920 by Nate Graham, on behalf of Arctic Lampyrid.
Committed on 25/04/2024 at 17:34.
Pushed by ngraham into branch 'Plasma/6.0'.

kded: Fix `launchState` setting not working

Before setting the initial state, we need to wait for the manager to
be operational.

`restoreAdapter()` is scheduled to be called after 1 second when
`adapterAdded` is emitted. Thus after applying `launchState` settings,
`saveState` should be called to avoid restoring to an incorrect state.

Signed-off-by: Arctic Lampyrid <ArcticLampyrid@outlook.com>
FIXED-IN: 6.0.5


(cherry picked from commit d71bfa54089b388a83473599a4dfce6ff06b4be6)

d145259e fix: `launchState` settings never works

M  +24   -0    src/kded/devicemonitor.cpp
M  +4    -0    src/kded/devicemonitor.h

https://invent.kde.org/plasma/bluedevil/-/commit/2cc4a2ed3e573df8760b8db6805a5396d89f3920