Function-keys-test on MEDION P15651/M15T notebook
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20210603, kernel 5.12.8, resource.c-patch with EDGE, LOW
20210604, kernel 5.12.9, resource.c-patch with LEVEL, LOW    <- retested all, same results

Fn+                      | showkey              | showkey -s          | acpi_listen  | effect
                                                                        (see bottom)  
 F1  (sleep)             | -                    | -                   | -            | -
 F2  (flight)            | -                    | -                   | -            | -
 F3  n/a                 | -                    | -                   | -            | -
 F4  n/a                 | -                    | -                   | -            | -
 F5  (brightness down)   | keycode 224 press                           
                           keycode 224 release  | 0xe0 0x4c 0xe0 0xcc | *1)          | works
 F6  (brightness up )    | keycode 225 press                           
                           keycode 225 release  | 0xe0 0x54 0xe0 0xd4 | *2)          | works
 F7  (LCD on/off)        | -                    | -                   | -            | works
 F8  (int./ext. display) | keycode 125 press                           
                           keycode  25 press                           
                           keycode  25 release                         
                           keycode 125 release  | 0xe0 0x5b 0x19 0x99  
                                                  0xe0 0xdb           | -            | works, shows KDE's
                                                                                       display switch menu
 F9  (touchpad on/off)   | keycode  29 press     
                           keycode 125 press     
                           keycode  85 press     
                           keycode  85 release   
                           keycode 125 release   
                           keycode  29 release  | 0x1d 0xe0 0x5b 0x76\ 
                                                  0xf6 0xe0 0xdb 0x9d | -            | -
 F10 (mute)              | keycode 113 press    | 0xe0 0x20           |              | \
 F11 (volume down)       | keycode 114 press    | 0xe0 0x2e           | *3)          |  } volume goes mad !
 F12 (volume up)         | keycode 115 press    | 0xe0 0x30           | *4)          | /  (ESCAPE stops madness)
                                                                                      
                         | showkey              | showkey -s          | acpi_listen  |

Side notes: 
- showkey prints as first line under X: "kb mode was ?UNKNOWN?", in tty1: "kb mode was UNICODE"
- the non-working Fn+ keys' functions are controllable by SW, e.g. under current KDE desktop

acpi_listen output:
*1) video/brightnessdown BRTDN 00000087 00000000
*2) video/brightnessup BRTUP 00000086 00000000
*3) button/volumedown VOLDN 00000080 00000000 K
*4) button/volumeup VOLUP 00000080 00000000 K