Here are some notes on running SF 9.X and Ubuntu 22. Please report back here on your progress/experience.
Install Ubuntu Server 22.04 LTS (incl. LAMP stack)
Install the database (e.g. MySQL) and create the ccnet, seafile & seahub databases
Install dependencies for Seafile 9.0.5 & Ubuntu Server 22.04:
sudo apt install python3 python3-{setuptools,pip} libmysqlclient-dev memcached libmemcached-dev libffi-dev
Install Python modules for Seafile 9.0.5 & Ubuntu Server 22.04:
sudo pip3 install django==3.2.* Pillow pylibmc captcha jinja2 sqlalchemy==1.4.3 django-pylibmc django-simple-captcha python3-ldap mysqlclient pycryptodome==3.12.0
Download & install Seafile Server 9.0.5
Install the package cffi 1.14.6 in the thirdpart folder, as suggested by Barolo:
sudo pip3 install --force-reinstall --upgrade --target <SOMEPATH>/seafile-server-9.0.5/seahub/thirdpart cffi==1.14.6
Run the installation script:
./<SOMEPATH>/seafile-server-9.0.5/setup-seafile-mysql.sh
Start Seafile Server & Seahub with ./seafile.sh and ./seahub.sh scripts