The answer is a subfolder should be added to the PATH variable, the working script is as follows

FROM rocker/rstudio:latest

# Install depencendcies

RUN apt-get update \

   && apt-get upgrade -y \

   && apt-get install -y 
 
#install tinytex 
RUN mkdir -p /tinytex
RUN Rscript -e ' install.packages("tinytex");tinytex::install_tinytex(dir="/tinytex",force=TRUE)'
ENV PATH="${PATH}:/tinytex/bin/x86_64-linux"

RUN tlmgr update --self
RUN tlmgr update --all
RUN tlmgr install \
        koma-script \
        caption \
        pgf \
        environ \
        tikzfill \
        tcolorbox \
        pdfcol