Found it!
Loaded installer in rescue mode, mounted and launched a shell in the installed system.
root@debian:/home/porridge# # touchpad does not work
root@debian:/home/porridge# dmesg|tail
[...]
[ 72.090285] EXT4-fs (dm-1): mounted filesystem fe627a07-f171-4074-b516-adb72b21bab0 r/w with ordered data mode. Quota mode: none.
root@debian:/home/porridge# modprobe pinctrl_meteorlake
root@debian:/home/porridge# # touchpad now works!
root@debian:/home/porridge# dmesg|tail
[...]
[ 72.090285] EXT4-fs (dm-1): mounted filesystem fe627a07-f171-4074-b516-adb72b21bab0 r/w with ordered data mode. Quota mode: none.
[ 660.196233] input: SNSL002D:00 2C2F:002D Mouse as /devices/pci0000:00/0000:00:15.0/i2c_designware.0/i2c-0/i2c-SNSL002D:00/0018:2C2F:002D.0001/input/input3
[ 660.196408] input: SNSL002D:00 2C2F:002D Touchpad as /devices/pci0000:00/0000:00:15.0/i2c_designware.0/i2c-0/i2c-SNSL002D:00/0018:2C2F:002D.0001/input/input4
[ 660.196476] hid-generic 0018:2C2F:002D.0001: input,hidraw0: I2C HID v1.00 Mouse [SNSL002D:00 2C2F:002D] on i2c-SNSL002D:00
[ 660.316781] input: SNSL002D:00 2C2F:002D Mouse as /devices/pci0000:00/0000:00:15.0/i2c_designware.0/i2c-0/i2c-SNSL002D:00/0018:2C2F:002D.0001/input/input6
[ 660.317289] input: SNSL002D:00 2C2F:002D Touchpad as /devices/pci0000:00/0000:00:15.0/i2c_designware.0/i2c-0/i2c-SNSL002D:00/0018:2C2F:002D.0001/input/input7
[ 660.317674] hid-multitouch 0018:2C2F:002D.0001: input,hidraw0: I2C HID v1.00 Mouse [SNSL002D:00 2C2F:002D] on i2c-SNSL002D:00
root@debian:/home/porridge#