Ansible has not published a package for focal in the ppa due to multiple build issues[1].
What exists for focal is ansible-base: the ansible project was restructured and split into ansible-base (later to be ansible-core) and a collection of modules and plugins which is now ansible[2]. In principle, for future releases ansible package would contain the collections and depend on ansible-base/ansible-core, which would replace the current ansible package. However, that work has not been done in the ppa, which neither provides the collections.
[1] https://github.com/ansible/ansible/issues/69203 [2] https://www.ansible.com/blog/ansible-3.0.0-qa
I guess there is also the possibility of pulling it from debian unstable. That feels a bit risky, but seems that we have all the dependencies in nabia to do it.