That's a bit of a sticky situation, and it's been on-going for years.
Don't just install libc6 2.35 alongside 2.31... it'll crash your system, most likely. You have to change the path of 2.35 (put it somewhere else than default), then change the path in the R programming language so it references that 'somewhere else'. That's a lot of work, and you don't have to do it.
Do this instead... follow the directions here:
https://cloud.r-project.org/bin/linux/ubuntu/
Issue this command:
sudo add-apt-repository ppa:c2d4u.team/c2d4u4.0+
Then find the package for Focal Fossa (which is Linux 20.04, which Zorin OS currently uses). It should attempt to use libc6 2.31.
Alternatively, you can try using the Debian packages:
https://cloud.r-project.org/bin/linux/debian/