I was trying to batch convert XLSX files to CSV on a multi-CPU system. However, libreoffice calc would only process one file at a time. Steps to reproduce: 1. /usr/lib64/libreoffice/program/soffice.bin --headless --convert-to 'xls:MS Excel 97' --outdir . /tmp/SXW1E_IS_1.xlsx & 2. /usr/lib64/libreoffice/program/soffice.bin --headless --convert-to 'xls:MS Excel 97' --outdir . /tmp/SXW1E_IS_2.xlsx & 3. top Expected results: Both jobs should have run in parallel. New systems will almost exclusively scale vertically (more CPUs, more cores, etc.), not allowing concurrent workloads is an obsolete paradigm.
https://ask.libreoffice.org/en/question/42975/how-can-i-run-multiple-instances-of-sofficebin-at-a-time/
In particular, what you want is the -env:UserInstallation option. Use a separate "user installation" (profile) directory for each instance and they should run in parallel.