I am trying R 4.1 in a schroot experimental container, while waiting that Bullseye's release will allow the package to be uploaded to Sid and the needed dependencies to be recompiled.

The schroot:

sudo debootstrap sid /srv/chroot/r-4.1 http://deb.debian.org/debian
sudo vi /etc/schroot/chroot.d/r-4.1
# Edit it to have something like
    [r-4.1]
    description=R 4.1 (experimental)
    type=directory
    directory=/srv/chroot/r-4.1
    users=  # Here put your username
    root-groups=root
    profile=desktop
    personality=linux
    preserve-environment=true
sudo schroot -c r-4.1
vi /etc/apt/sources.list # To add the experimental distribution
apt update
apt install sudo vim wget
exit

Installation of R:

schroot -c r-4.1
sudo apt install r-base/experimental -texperimental
sudo apt install -texperimental pandoc libxml2-dev libcurl4-openssl-dev git libssl-dev texlive

And RStudio (preview version needed)

wget https://s3.amazonaws.com/rstudio-ide-build/desktop/bionic/amd64/rstudio-1.4.1714-amd64.deb
sudo apt install libnss3 libasound2
sudo dpkg -i rstudio-1.4.1714-amd64.deb 
sudo apt -f install -texperimental