Install tls and http2. I see that you have everything installed. This is for clarification.
pip install -U 'Twisted[tls,http2]'
You can use your own privateKey and certKey for testing.
I will run commands in the /home/user/Documents/ssl/
openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout selfsigned.key -out selfsigned.crt
Run the application
daphne -e ssl:8000:privateKey=/home/user/Documents/ssl/selfsigned.key:certKey=/home/user/Documents/ssl/selfsigned.crt myapp.asgi:application
Output
user@debian:~/Documents/pythonWeb/myapp$ daphne -e ssl:8000:privateKey=/home/user/Documents/ssl/selfsigned.key:certKey=/home/user/Documents/ssl/selfsigned.crt myapp.asgi:application
2022-02-04 18:49:12,726 INFO Starting server at ssl:8000:privateKey=/home/user/Documents/ssl/selfsigned.key:certKey=/home/user/Documents/ssl/selfsigned.crt
2022-02-04 18:49:12,726 INFO HTTP/2 support enabled
2022-02-04 18:49:12,726 INFO Configuring endpoint ssl:8000:privateKey=/home/user/Documents/ssl/selfsigned.key:certKey=/home/user/Documents/ssl/selfsigned.crt
2022-02-04 18:49:12,733 INFO Listening on TCP address 0.0.0.0:8000
2022-02-04 18:49:27,644 INFO file_cache is only supported with oauth2client<4.0.0
192.168.1.106:50128 - - [04/Feb/2022:18:49:32] "GET /stream_1/" 200 2510
192.168.1.106:58251 - - [04/Feb/2022:18:49:32] "WSCONNECTING /ws/chat/stream_1/" - -
connect
If you have ".pem" files from Let's Encrypt, paste them in place of the self-signed ones.