Ran into this on Ubuntu 21.10 (impish), because I had borked my installation paths thinking pgadmin4 wasn't fully installed when it was.
The error is because it is assuming python3.8 is installed (21.10 comes with python3.9) , but it isn't, so all the symlinks and virtual env fails. But this is happening because you've installed a version of pgadmin4 that doesn't match your Ubuntu version.
garrett@garrett-external:/etc/apt/sources.list.d$ ls
deadsnakes-ubuntu-ppa-impish.list pgadmin4.list.save pgdg.list.save
pgadmin4.list pgdg.list
##Looking at pgadmin4.list.save , I see I had at least tried to use
# hirsute 's repo:
garrett@garrett-external:/etc/apt/sources.list.d$ cat pgadmin4.list.save
deb https://ftp.postgresql.org/pub/pgadmin/pgadmin4/apt/hirsute pgadmin4 main
##I'm thinking this is overriding the correct impish repos, so I'll
# try deleting that file, purging the installation and re-installing:
garrett@garrett-external:/etc/apt/sources.list.d$ ls
deadsnakes-ubuntu-ppa-impish.list pgadmin4.list pgadmin4.list.save pgdg.list pgdg.list.save
garrett@garrett-external:/etc/apt/sources.list.d$ sudo rm pgadmin4.list.save
##double check that the pgadmin4 sources are correct...
garrett@garrett-external:/etc/apt/sources.list.d$ ls
deadsnakes-ubuntu-ppa-impish.list pgadmin4.list pgdg.list pgdg.list.save
garrett@garrett-external:/etc/apt/sources.list.d$ cat pgadmin4.list
deb https://ftp.postgresql.org/pub/pgadmin/pgadmin4/apt/focal pgadmin4 main
##^ok definitely the problem...should fix that....
garrett@garrett-external:/etc/apt/sources.list.d$ sudo sed -i 's/focal/impish/g' /etc/apt/sources.list.d/pgadmin4.list
garrett@garrett-external:/etc/apt/sources.list.d$ cat ./pgadmin4.list
deb https://ftp.postgresql.org/pub/pgadmin/pgadmin4/apt/impish pgadmin4 main
##uninstall pgadmin4
garrett@garrett-external:/etc/apt/sources.list.d$ sudo apt purge pgadmin4
garrett@garrett-external:/etc/apt/sources.list.d$ sudo apt autoremove
##reinstall pgadmin4
garrett@garrett-external:/etc/apt/sources.list.d$ sudo apt update && sudo apt install pgadmin4
And now it works fine
EDIT: DON'T GO DOWN THE RABBIT HOLE BELOW
Workaround: Manually install python3.8 using the deadsnakes PPA and some temporary apt cache updating trickery
#first add deadsnakes ppa...
$ sudo add-apt-repository ppa:deadsnakes
# Following the gist of https://brennan.io/2021/06/21/deadsnakes-hirsute/ ,
# update the deadsnakes ppa's app repos to look at the past 2 LTS versions
$ sudo vim /etc/apt/sources.list.d/deadsnakes-ubuntu-ppa-impish.list
---> change
'deb http://ppa.launchpad.net/deadsnakes/ppa/ubuntu/ impish main' to
'deb http://ppa.launchpad.net/deadsnakes/ppa/ubuntu/ bionic main' , also add
'deb http://ppa.launchpad.net/deadsnakes/ppa/ubuntu/ focal main'
#Add the following rules which blacklist all packages from
# the repos, and then selectively enable Python versions from the correct
# locations. This can be put in any filename within the directory
# /etc/apt/preferences.d/ (I named mine deadsnakes_pref)
Explanation: Prevent installing from deadsnakes repo.
Package: *
Pin: release o=LP-PPA-deadsnakes
Pin-Priority: 1
Explanation: Allow installing python 3.{6,7} from deadsnakes/focal
Package: *python3.6* *python3.7*
Pin: release o=LP-PPA-deadsnakes,n=focal
Pin-Priority: 500
Explanation: Allow installing python 3.8 from deadsnakes/bionic
Package: *python3.8*
Pin: release o=LP-PPA-deadsnakes,n=bionic
Pin-Priority: 500
##temporarily change all your sources to bionic, so the python3.8
#dependencies will be met
$ sudo sed -i 's/impish/bionic/g' /etc/apt/sources.list
## try to update the apt cache and install python3.8 . You'll get yelled
# at for not having the proper key ring:
****************
W: GPG error: http://us.archive.ubuntu.com/ubuntu bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4FE6ACC0B21F32
E: The repository 'http://us.archive.ubuntu.com/ubuntu bionic InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
****************
## so following
## https://askubuntu.com/questions/13065/how-do-i-fix-the-gpg-error-no-pubkey
## , I add the key
$ sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3B4FE6ACC0B21F32
# now this should work
$ sudo apt update && sudo apt install python3.8
#after we're done, don't forget to change back your sources
$ sudo sed -i 's/bionic/impish/g' /etc/apt/sources.list
$ sudo apt update
#And now pgadmin4 should work. If you want to run it from the terminal,
# add this line to your ~/.bash_aliases file:
alias pgadmin4='/usr/pgadmin4/bin/pgadmin4'
