If you are installing dolfin from source, you should be able to follow How to install dolfin on Ubuntn-20.04 from source
I still recommend using docker, as you can then skip all installation by running
docker run -ti -p 127.0.0.1:8000:8000 -v $(pwd):/home/fenics/shared -w /home/fenics/shared quay.io/fenicsproject/stable:current