The tinytex package is a LaTeX distribution intended for R users. It is not inherently difficult to install, but does have some gotchas to know about to get it working. The docker instructions to install the package in a Domino environment are...
# install tinytex
RUN Rscript -e 'tinytex::install_tinytex()'
# Setting Environment Variables within domino workspace
RUN echo 'export PATH=/home/ubuntu/bin:$PATH' >> /home/ubuntu/.domino-defaults
Tinytex needs to install as the ubuntu user instead of as the root user since tinytex appears to put its directories in the installing user's home directory, instead of on a system directory.
So for root, the files get placed in /root/bin. Even if that is on the PATH the ubuntu user cannot access files in /root/bin. Because this is a non system path, you also have to add ~/bin to the PATH variable.
When you start a workspace, under the hood you are the ubuntu user, so with a package install like this that places files in the installing user's home directory, the install should be done as the ubuntu user.