The built-in microphone of the laptop is working perfectly with the corresponding modules for AMD Raphael / RPL compiled as modules.
$ lsmod | grep snd
snd_seq_dummy 12288 0
snd_hrtimer 12288 1
snd_seq 114688 7 snd_seq_dummy
snd_seq_device 16384 1 snd_seq
snd_soc_dmic 12288 1
snd_ps_pdm_dma 12288 1
snd_soc_ps_mach 12288 1
snd_ctl_led 24576 0
snd_soc_core 421888 3 snd_soc_ps_mach,snd_ps_pdm_dma,snd_soc_dmic
snd_hda_codec_realtek 192512 1
snd_compress 28672 1 snd_soc_core
snd_hda_codec_generic 114688 1 snd_hda_codec_realtek
snd_hda_codec_hdmi 94208 1
ledtrig_audio 12288 3 snd_ctl_led,snd_hda_codec_generic,thinkpad_acpi
snd_pci_ps 24576 0
snd_hda_intel 61440 2
snd_intel_dspcfg 36864 1 snd_hda_intel
snd_rpl_pci_acp6x 16384 0
snd_intel_sdw_acpi 16384 1 snd_intel_dspcfg
snd_acp_pci 12288 0
snd_hda_codec 225280 4 snd_hda_codec_generic,snd_hda_codec_hdmi,snd_hda_intel,snd_hda_codec_realtek
snd_acp_legacy_common 16384 1 snd_acp_pci
snd_hda_core 147456 5 snd_hda_codec_generic,snd_hda_codec_hdmi,snd_hda_intel,snd_hda_codec,snd_hda_codec_realtek
snd_pci_acp6x 16384 0
snd_hwdep 20480 1 snd_hda_codec
snd_pcm 192512 9 snd_hda_codec_hdmi,snd_pci_acp6x,snd_hda_intel,snd_hda_codec,snd_ps_pdm_dma,snd_compress,snd_soc_core,snd_hda_core,snd_pci_ps
snd_pci_acp5x 16384 0
snd_rn_pci_acp3x 20480 0
snd_timer 53248 3 snd_seq,snd_hrtimer,snd_pcm
snd_acp_config 16384 5 snd_rn_pci_acp3x,snd_pci_acp6x,snd_pci_acp5x,snd_acp_pci,snd_pci_ps
snd 155648 22 snd_ctl_led,snd_hda_codec_generic,snd_seq,snd_seq_device,snd_hda_codec_hdmi,snd_hwdep,snd_hda_intel,snd_hda_codec,snd_hda_codec_realtek,snd_timer,snd_compress,thinkpad_acpi,snd_soc_core,snd_pcm
snd_soc_acpi 16384 1 snd_acp_config
soundcore 16384 2 snd_ctl_led,snd
snd_pci_acp3x 16384 0
So I can confirm compiling the kernel with the kconfig switches CONFIG_SND_SOC_AMD_RPL_ACP6x=m and CONFIG_SND_SOC_AMD_ACP_PCI=m (which is required according to the help text of the other switch) enables my hardware.
Please include these modules in future Debian Linux kernel packages.