Debian stopped using my Intel i915 GPU after upgrade to Trixie. How to fix?

My notebook, an older Apple MacBookAir 13" with Intel Core i7 an Intel HD Graphics 5000, used to work fine before the upgrade to Trixie (Debian GNU/Linux 13). Now, after the upgrade, all rendering is done using the CPU instead of the GPU. This is annoying and makes the machine feel slow. I would like to have accelerated hardware rendering back, but I don't know where to start troubleshooting this. All relevant packages seems to be installed. The GPU is detected. But llvmpipe is used for all rendering instead. System info:

#uname -a
Linux mymachine 6.12.38+deb13-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.12.38-1 (2025-07-16) x86_64 GNU/Linux

# ls -l /dev/dri
total 0
drwxr-xr-x  2 root root         80 Jul 28 01:32 by-path
crw-rw----+ 1 root video  226,   0 Jul 30 13:06 card0
crw-rw----+ 1 root render 226, 128 Jul 28 01:32 renderD128

# LANG=C inxi -Fxxxrzc0
(...)
Graphics:
  Device-1: Intel Haswell-ULT Integrated Graphics vendor: Apple driver: i915
    v: kernel arch: Gen-7.5 ports: active: DP-1,eDP-1
    empty: DP-2,HDMI-A-1,HDMI-A-2 bus-ID: 00:02.0 chip-ID: 8086:0a26
    class-ID: 0300
  Display: x11 server: X.Org v: 21.1.16 with: Xwayland v: 24.1.6
    compositor: xfwm4 v: 4.20.0 driver: X: loaded: intel dri: swrast gpu: i915
    display-ID: :0.0 screens: 1
  Screen-1: 0 s-res: 3360x1080 s-dpi: 96 s-size: 890x286mm (35.04x11.26")
    s-diag: 935mm (36.8")
  Monitor-1: DP-1 mapped: DP1 pos: right model: Dell P2214H serial: 
    res: mode: 1920x1080 hz: 60 scale: 100% (1) dpi: 102
    size: 480x270mm (18.9x10.63") diag: 547mm (21.5") modes: max: 1920x1080
    min: 720x400
  Monitor-2: eDP-1 mapped: eDP1 pos: primary,left model: Apple Color LCD
    res: mode: 1440x900 hz: 60 scale: 100% (1) dpi: 126
    size: 290x180mm (11.42x7.09") diag: 341mm (13.4") modes: 1440x900
  API: EGL v: 1.5 hw: drv: intel crocus platforms: device: 0 drv: crocus
    device: 1 drv: swrast gbm: drv: crocus surfaceless: drv: crocus x11:
    drv: swrast inactive: wayland
  API: OpenGL v: 4.6 compat-v: 4.5 vendor: mesa v: 25.0.7-2 glx-v: 1.4
    direct-render: yes renderer: llvmpipe (LLVM 19.1.7 256 bits)
    device-ID: ffffffff:ffffffff
  Info: Tools: api: eglinfo,glxinfo de: xfce4-display-settings gpu: gputop,
    intel_gpu_top, lsgpu wl: wayland-info x11: xdriinfo, xdpyinfo, xprop,
    xrandr
(...)

# grep -e WW -e EE /var/log/Xorg.0.log
[     8.834] Current Operating System: Linux MBAirFronczek 6.12.38+deb13-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.12.38-1 (2025-07-16) x86_64
	(WW) warning, (EE) error, (NI) not implemented, (??) unknown.
[     8.905] (II) Initializing extension MIT-SCREEN-SAVER
[     8.907] (EE) AIGLX error: dlopen of /usr/lib/x86_64-linux-gnu/dri/i965_dri.so failed (/usr/lib/x86_64-linux-gnu/dri/i965_dri.so: cannot open shared object file: No such file or directory)
[     8.907] (EE) AIGLX error: unable to load driver i965
[    10.905] (WW) intel(0): Output eDP1: Strange aspect ratio (30/179), consider adding a quirk
[    34.463] (EE) event8  - bcm5974: kernel bug: Touch jump detected and discarded.
[  1267.808] (EE) event8  - bcm5974: kernel bug: Touch jump detected and discarded.
[  1710.292] (EE) event8  - bcm5974: kernel bug: Touch jump detected and discarded.
[  3134.814] (EE) event8  - bcm5974: kernel bug: Touch jump detected and discarded.
[ 11649.438] (EE) event8  - bcm5974: kernel bug: Touch jump detected and discarded.
[ 11649.438] (EE) event8  - bcm5974: WARNING: log rate limit exceeded (5 msgs per 24h). Discarding future messages.
[ 22436.276] (EE) event8  - bcm5974: client bug: event processing lagging behind by 32ms, your system is too slow
[ 27719.291] (EE) event1  - Power Button: client bug: event processing lagging behind by 454ms, your system is too slow
[ 27719.291] (EE) event3  - Power Button: client bug: event processing lagging behind by 454ms, your system is too slow
[ 27719.291] (EE) event4  - Apple Inc. Apple Internal Keyboard / Trackpad: client bug: event processing lagging behind by 382ms, your system is too slow
[ 41075.009] (EE) event1  - Power Button: client bug: event processing lagging behind by 1040ms, your system is too slow
[ 41075.009] (EE) event3  - Power Button: client bug: event processing lagging behind by 1040ms, your system is too slow
[ 60993.939] (EE) event8  - bcm5974: kernel bug: Touch jump detected and discarded.
[ 61022.742] (EE) event8  - bcm5974: kernel bug: Touch jump detected and discarded.
[ 61456.304] (EE) event8  - bcm5974: kernel bug: Touch jump detected and discarded.
[ 62833.756] (EE) event8  - bcm5974: kernel bug: Touch jump detected and discarded.
[ 63129.269] (EE) event8  - bcm5974: kernel bug: Touch jump detected and discarded.
[ 63129.269] (EE) event8  - bcm5974: WARNING: log rate limit exceeded (5 msgs per 24h). Discarding future messages.
[ 67081.490] (EE) event8  - bcm5974: client bug: event processing lagging behind by 28ms, your system is too slow
[ 69447.954] (EE) event8  - bcm5974: client bug: event processing lagging behind by 23ms, your system is too slow
[ 69983.294] (EE) event8  - bcm5974: client bug: event processing lagging behind by 23ms, your system is too slow
[ 78710.772] (EE) event8  - bcm5974: kernel bug: Touch jump detected and discarded.
[ 84611.777] (EE) event8  - bcm5974: client bug: event processing lagging behind by 25ms, your system is too slow

There is no /etc/X11/xorg.conf on my system. /etc/X11/xorg.conf.d/ contains a file called 20-displaylink.conf:

Section "Device"
    Identifier  "Intel"
    Driver      "intel"
EndSection

Plus, another file called 90-xpra-virtual.conf which was automatically created:

# Ignore all xpra virtual devices by default,
# these will be enabled explicitly when needed.
Section "InputClass"
        Identifier "xpra-virtual-device"
        MatchProduct "Xpra"
        Option "Ignore" "true"
EndSection

A *systematic troubleshooting guide* would be most helpful/appreciated. Unfortunately, I could not find a suiable one online = one that is specific to this piece of hardware and one that does include a fix, not only diagnosis. P.S.: I have another older computer (an older MacMini) that also has an Intel chipset/GPU, also uses the i915 driver and suffers from the same type of problem (renderer: llvmpipe instead of GPU, even though GPU seems to be "recognzied"). So I am pretty sure that this is related to the upgrade to Trixie/Debian testing. Other than that, I have no idea as where to start troubleshooting this.