Resolved it by installing fonts:

apk --update --upgrade --no-cache add fontconfig ttf-freefont font-noto term
inus-font \
    && fc-cache -f \
    && fc-list | sort

If you want to add custom fonts, try adding them under /usr/share/fonts/Additional

references

• https://github.com/orzih/mkdocs-with-pdf/blob/c97272aa92440789de2d93a6e78ae42b9c441eef/docker/mkdocs-with-pdf/alpine/Dockerfile#L25-L29
• https://github.com/orzih/mkdocs-with-pdf/issues/50#issuecomment-767140386