This looks very similar to the issue I have been having.
In particular, both of our installation attempts have an error resembling:
2021-12-22 15:11:25,539: WARNING - Fatal Python error: GC object already tracked
2021-12-22 15:11:25,540: DEBUG -
2021-12-22 15:11:25,540: WARNING - Current thread 0x00007f3eaa64c740 (most recent call first):
2021-12-22 15:11:25,541: WARNING - File "/opt/yunohost/matrix-synapse/lib/python3.7/site-packages/attr/validators.py", line 356 in __call__
2021-12-22 15:11:25,541: WARNING - File "<attrs generated init synapse.types.RoomStreamToken>", line 12 in __init__
2021-12-22 15:11:25,542: WARNING - File "/opt/yunohost/matrix-synapse/lib/python3.7/site-packages/synapse/types.py", line 676 in <module>
2021-12-22 15:11:25,543: WARNING - File "<frozen importlib._bootstrap>", line 219 in _call_with_frames_removed
2021-12-22 15:11:25,543: WARNING - File "<frozen importlib._bootstrap_external>", line 728 in exec_module
2021-12-22 15:11:25,544: WARNING - File "<frozen importlib._bootstrap>", line 677 in _load_unlocked
2021-12-22 15:11:25,544: WARNING - File "<frozen importlib._bootstrap>", line 967 in _find_and_load_unlocked
2021-12-22 15:11:25,545: WARNING - File "<frozen importlib._bootstrap>", line 983 in _find_and_load
2021-12-22 15:11:25,546: WARNING - File "/opt/yunohost/matrix-synapse/lib/python3.7/site-packages/synapse/events/__init__.py", line 39 in <module>
2021-12-22 15:11:25,547: WARNING - File "<frozen importlib._bootstrap>", line 219 in _call_with_frames_removed
2021-12-22 15:11:25,547: WARNING - File "<frozen importlib._bootstrap_external>", line 728 in exec_module
2021-12-22 15:11:25,548: WARNING - File "<frozen importlib._bootstrap>", line 677 in _load_unlocked
2021-12-22 15:11:25,548: WARNING - File "<frozen importlib._bootstrap>", line 967 in _find_and_load_unlocked
2021-12-22 15:11:25,549: WARNING - File "<frozen importlib._bootstrap>", line 983 in _find_and_load
2021-12-22 15:11:25,549: WARNING - File "<frozen importlib._bootstrap>", line 219 in _call_with_frames_removed
2021-12-22 15:11:25,550: WARNING - File "<frozen importlib._bootstrap>", line 1035 in _handle_fromlist
2021-12-22 15:11:25,551: WARNING - File "/opt/yunohost/matrix-synapse/lib/python3.7/site-packages/synapse/app/homeserver.py", line 28 in <module>
2021-12-22 15:11:25,551: WARNING - File "/usr/lib/python3.7/runpy.py", line 85 in _run_code
2021-12-22 15:11:25,552: WARNING - File "/usr/lib/python3.7/runpy.py", line 193 in _run_module_as_main
2021-12-22 15:11:25,555: WARNING - ./install: line 217: 31038 Aborted python -m synapse.app.homeserver --keys-directory /etc/matrix-$app/ --generate-config --generate-keys --server-name $server_name --report-stats=no -c homeserver.yml