failure when installing on pi4 ubuntu server lts 20.04

when installing the mistborn script on a raspberry pi with ubuntu server LTS 32 bits or 64bits the following error occurs when installing docker:

Package python is not available, but is referred to by another package. This may mean that the package is missing, has been obsoleted, or is only available from another source However the following packages replace it: python2-minimal python2 dh-python 2to3 python-is-python3

E: Package 'python' has no installation candidate