How do I find out if I've got a built-in bluetooth-adapter?

Try this (Bluetooth uses the uSB bus).

dmesg | grep -i blue

I seem to remember you disabled it some time ago because of a 100% CPU load.

If you are still using the same system, then you might try:

sudo systemctl enable bluetooth.service

and restart your system.

Thanks for your swift replies.

dmesg | grep -i blue

yields

[ 1.887309] usb 3-11: Product: Bluetooth Radio
[ 8.003177] thinkpad_acpi: rfkill switch tpacpi_bluetooth_sw: radio is unblocked
[ 8.157490] Bluetooth: Core ver 2.21
[ 8.157508] Bluetooth: HCI device and connection manager initialized
[ 8.157511] Bluetooth: HCI socket layer initialized
[ 8.157514] Bluetooth: L2CAP socket layer initialized
[ 8.157518] Bluetooth: SCO socket layer initialized
[ 8.261498] Bluetooth: hci0: rtl: examining hci_ver=06 hci_rev=000a lmp_ver=06 lmp_subver=8761
[ 8.261500] Bluetooth: hci0: rtl: loading /*(DEBLOBBED)*/
[ 8.282296] bluetooth hci0: Direct firmware load failed with error -2
[ 8.282300] Bluetooth: hci0: Failed to load /*(DEBLOBBED)*/
[ 8.659468] Bluetooth: hci0: rtl: examining hci_ver=06 hci_rev=000a lmp_ver=06 lmp_subver=8761
[ 8.659472] Bluetooth: hci0: rtl: loading /*(DEBLOBBED)*/
[ 8.659488] bluetooth hci0: Direct firmware load failed with error -2
[ 8.659490] Bluetooth: hci0: Failed to load /*(DEBLOBBED)*/
[ 14.354424] Bluetooth: BNEP (Ethernet Emulation) ver 1.3
[ 14.354429] Bluetooth: BNEP filters: protocol multicast
[ 14.354434] Bluetooth: BNEP socket layer initialized

sudo systemctl enable bluetooth.service and restart don't help. Using blueman, "add new device" results in the error message "no adapter found".

You might want to try the following command, that will check the status of your bluetooth device and tell you whether it is soft or hard blocked:

rfkill

You might need to install rfkill first:

sudo apt install rfkill

EDIT: the correct command to re-enable bluetooth might in fact be:

sudo systemctl enable bluetooth

"rfkill list" produces:

0: tpacpi_bluetooth_sw: Bluetooth
Soft blocked: no
Hard blocked: no
1: hci0: Bluetooth
Soft blocked: no
Hard blocked: no

"sudo systemctl enable bluetooth" and
"sudo systemctl enable bluetooth.service" both produce:

Synchronizing state of bluetooth.service with SysV init with /lib/systemd/systemd-sysv-install...
Executing /lib/systemd/systemd-sysv-install enable bluetooth

After restart, blueman still produces the error message "no bluetooth adapter found".

PS: How do I edit my comments so that code or paste from the terminal appear nicely like in your message?

The Bluetooth may require proprietary firmware.

How do I find out if that bluetooth needs proprietary firmware?

Thanks.

~$ lspci
[...]
02:00.0 Network controller: Realtek Semiconductor Co., Ltd. RTL8192EE PCIe Wireless Network Adapter

h-node.org list the Realtex RTL8192SE wifi card as not working and also I never got my interal wifi working with free software. Do you agree that also bluetooth won't work for the same reason? In general, does the Network controller control both wifi and bluetooth?

"Do you agree that also bluetooth won't work for the same reason?"

Is a fair assumption, I'd imagine.

"In general, does the Network controller control both wifi and bluetooth?"

Appears that your RTL8192EE doesn't, I don't see anything about bluetooth on https://www.realtek.com/en/products/communications-network-ics/item/rtl8192ee

sometimes the proceeding command can be useful to find hardware related information

sudo lshw -sanitize

Hey guys (and girls?) ;-)

Thanks very much for your help. I'm about to accept there is no built-in adapter and consider getting a 'free' one, but:
~$ sudo lshw -sanitize
[...]
*-usb:1
Beschreibung: Bluetooth-Schnittstelle
Produkt: Bluetooth Radio
Hersteller: Realtek
Physische ID: b
Bus-Informationen: usb@3:b
Version: 2.00
Seriennummer: [REMOVED]
Fähigkeiten: bluetooth usb-2.10
Konfiguration: driver=btusb maxpower=500mA speed=12Mbit/s

So there seems to be a built-in adapter, right? How do I proceed from here?

Best regards, stay safe!

Please help me to understand:
/*(DEBLOBBED)*/ = free as in freedom
proprietary firmware = unfree

Did you mean the BLOBBED firmware? I don't quite get it. Is there firmware that has been freed of anything unfree? And if so, where do I get it?

I probably haven't understood what you meant by sending me the link.

Hey guys

Thanks a lot for the clarification. I hadn't been aware that

/*(DEBLOBBED)*/

was a placeholder.

I'm going to get new hardware I think.

Thanks again & stay safe

anatom