I'm also running Ubuntu 18.04. As ansible is a python package you can update via python like this
pip3 install --user --upgrade pip
pip3 install --user ansible
hash -r
You then get:
$ ansible --version
ansible 2.10.8
config file = /home/user/git/ansible-win/ansible.cfg
configured module search path = ['/home/user/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
ansible python module location = /home/user/.local/lib/python3.6/site-packages/ansible
executable location = /home/user/.local/bin/ansible
python version = 3.6.9 (default, Jan 26 2021, 15:33:00) [GCC 8.4.0]