[R-sig-Debian] Install R 4 on Chromebook (unmet dependencies)

[Luigi Marongiu]

Hello,
I have tried to upgrade R to 4.0. I have added `deb
http://cloud.r-project.org/bin/linux/debian buster-cran40/` to
`/etc/apt/sources.list` (but I removed cran35). Btu when I run
`apt-get update; apt-get install r-base r-base-dev` I get an error. I
think it depends on r-base-core, since it depends on these obsolete
libraries:
```
$ sudo apt-get install r-base-core
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 r-base-core : Depends: libc6 (>= 2.27) but 2.24-11+deb9u4 is to be installed
               Depends: libcurl4 (>= 7.28.0) but it is not installable
               Depends: libgfortran5 (>= 8) but it is not installable
               Depends: libicu63 (>= 63.1-1~) but it is not installable
               Depends: libpcre2-8-0 (>= 10.32) but it is not going to
be installed
               Recommends: r-recommended but it is not going to be installed
               Recommends: r-base-dev but it is not going to be installed
               Recommends: r-doc-html but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
```
How can I upgrade these libraries on Chromebook?
Thank you