pgadmin4 - which python

I want to install pgadmin4 with Mint 19.3. and get this:

> thomas@Epsil192:~/Downloads/pgadmin4/pgadmin4-4.27/runtime$ sudo qmake
> Project MESSAGE: ==================================
> Project MESSAGE: Configuring the pgAdmin 4 runtime.
> Project MESSAGE: ==================================
> Project MESSAGE: Qt version: 5.12.8
> Project ERROR: The PGADMIN_PYTHON_DIR environment variable is not set. Please set it to a directory path under which Python 3.4 or later has been installed and try again.
> thomas@Epsil192:~/Downloads/pgadmin4/pgadmin4-4.27/runtime$ echo $PGADMIN_PYTHON_DIR
> /usr/lib/python3.8/

I don't understand why $PGADMIN_PYTHON_DIR is not found.

Egon