Не удается установить R 4.X ​​на Ubuntu 20.04

Я пытаюсь обновить R на своей Ubuntu 20.04 (новое обновление от 16.04).

Поэтому я удаляю предыдущую версию R следующим образом:

sudo apt-get purge r-base* r-recommended r-cran-*    
sudo apt autoremove

После этого я обновляю свой /etc/apt/sources.list, добавляя хороший репозиторий

deb https://cloud.r-project.org/bin/linux/ubuntu focal-cran40/

И правильный ключ:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys E298A3A825C0D65DFD57CBB651716619E084DAB9

Но я получаю ошибка при обновлении sources.list :

sudo apt-get update
Ign :10 https://cloud.r-project.org/bin/linux/ubuntu focal-cran40/ InRelease
Err :11 https://cloud.r-project.org/bin/linux/ubuntu focal-cran40/ Release
  Could not wait for server fd - select (11: Ressource temporairement non disponible) [IP : xxx.xxx.xxx.xxx xxxx]
Lecture des listes de paquets... Fait
W: Le fichier configuré « partener/source/Sources » ne sera pas pris en compte car le dépôt « http://archive.canonical.com/ubuntu focal InRelease » ne dispose pas de la source « partener » (erreur de saisie dans sources.list ?)
E: Le dépôt https://cloud.r-project.org/bin/linux/ubuntu focal-cran40/ Release n'a pas de fichier Release.

На работе сижу за прокси. Итак, параметры прокси указаны в параметрах сети в системных параметрах, но также и для apt. (файл 80proxy в /etc/apt/apt.conf.d/)

С этой конфигурацией доступна только версия R 3.6:

apt-cache policy r-base r-base-core r-base-dev r-recommended
r-base:
  Installé : (aucun)
  Candidat : 3.6.3-2
 Table de version :
     3.6.3-2 500
        500 http://fr.archive.ubuntu.com/ubuntu focal/universe amd64 Packages
        500 http://fr.archive.ubuntu.com/ubuntu focal/universe i386 Packages
r-base-core:
  Installé : (aucun)
  Candidat : 3.6.3-2
 Table de version :
     3.6.3-2 500
        500 http://fr.archive.ubuntu.com/ubuntu focal/universe amd64 Packages
r-base-dev:
  Installé : (aucun)
  Candidat : 3.6.3-2
 Table de version :
     3.6.3-2 500
        500 http://fr.archive.ubuntu.com/ubuntu focal/universe amd64 Packages
        500 http://fr.archive.ubuntu.com/ubuntu focal/universe i386 Packages
r-recommended:
  Installé : (aucun)
  Candidat : 3.6.3-2
 Table de version :
     3.6.3-2 500
        500 http://fr.archive.ubuntu.com/ubuntu focal/universe amd64 Packages
        500 http://fr.archive.ubuntu.com/ubuntu focal/universe i386 Packages

У меня есть ноутбук с обновленной Ubuntu 20.04 и тем же списком sources.list и Я не встречаю ошибки из домашней сети.

Подозреваю, что ошибка связана с параметрами прокси, но не уверен. Не могли бы вы помочь успешно настроить и установить последнюю версию R?

Большое спасибо за помощь.

Мои источники.список:

 more /etc/apt/sources.list
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://fr.archive.ubuntu.com/ubuntu/ focal main restricted
deb-src http://fr.archive.ubuntu.com/ubuntu/ focal main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://fr.archive.ubuntu.com/ubuntu/ focal-updates main restricted
deb-src http://fr.archive.ubuntu.com/ubuntu/ focal-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://fr.archive.ubuntu.com/ubuntu/ focal universe
deb-src http://fr.archive.ubuntu.com/ubuntu/ focal universe
deb http://fr.archive.ubuntu.com/ubuntu/ focal-updates universe
deb-src http://fr.archive.ubuntu.com/ubuntu/ focal-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu 
## team, and may not be under a free licence. Please satisfy yourself as to 
## your rights to use the software. Also, please note that software in 
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://fr.archive.ubuntu.com/ubuntu/ focal multiverse
deb-src http://fr.archive.ubuntu.com/ubuntu/ focal multiverse
deb http://fr.archive.ubuntu.com/ubuntu/ focal-updates multiverse
deb-src http://fr.archive.ubuntu.com/ubuntu/ focal-updates multiverse

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://fr.archive.ubuntu.com/ubuntu/ focal-backports main restricted univers
e multiverse
deb-src http://fr.archive.ubuntu.com/ubuntu/ focal-backports main restricted uni
verse multiverse

deb http://security.ubuntu.com/ubuntu focal-security main restricted
deb-src http://security.ubuntu.com/ubuntu focal-security main restricted
deb http://security.ubuntu.com/ubuntu focal-security universe
deb-src http://security.ubuntu.com/ubuntu focal-security universe
deb http://security.ubuntu.com/ubuntu focal-security multiverse
deb-src http://security.ubuntu.com/ubuntu focal-security multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
deb http://archive.canonical.com/ubuntu focal partner
deb-src http://archive.canonical.com/ubuntu focal partner

## The Comprehensive R Archive Network

deb https://cloud.r-project.org/bin/linux/ubuntu focal-cran40/
# deb-src https://cloud.r-project.org/bin/linux/ubuntu focal-cran40/