No microphone / headset function for Pixel Buds A-Series with pulseaudio / Ubuntu 20.04.3

I am using Ubuntu 20.04.3 LTS and trying to use my Pixel Buds A-Series as headset. It works perfectly fine as audio sink / headphones, but I can't switch the Profile to 'headset' (in order to get the microphone to work)

It detects the profiles a2dp_sink and headset_head_unit but the later is shown with 'avaliable:no'

when I try to switch the profile to headset_head_unit:

pactl set-card-profile 24 headset_head_unit

i get:

Failure: Input/Output error

Here is the output of pactl (personal information replaced with xxxx)

pactl list

Card #24 Name: bluez_card.xxxxxx Driver: module-bluez5-device.c Owner Module: 51 Properties: device.description = "xxxxx Pixel Buds A-Series" device.string = "xxxxxx" device.api = "bluez" device.class = "sound" device.bus = "bluetooth" device.form_factor = "headset" bluez.path = "/org/bluez/hci0/dev_xxxxx" bluez.class = "0x240404" bluez.alias = "xxx's Pixel Buds A-Series" device.icon_name = "audio-headset-bluetooth" device.intended_roles = "phone" Profiles: a2dp_sink: High Fidelity Playback (A2DP Sink) (sinks: 1, sources: 0, priority: 40, available: yes) headset_head_unit: Headset Head Unit (HSP/HFP) (sinks: 1, sources: 1, priority: 30, available: no) off: Off (sinks: 0, sources: 0, priority: 0, available: yes) Active Profile: a2dp_sink Ports: headset-output: Headset (priority: 0, latency offset: 0 usec, available) Part of profile(s): a2dp_sink, headset_head_unit headset-input: Headset (priority: 0, latency offset: 0 usec, not available) Part of profile(s): headset_head_unit

Know someone who can answer? Share a link to this question via email, Twitter, or Facebook.