I think that there is an easier way to install several versions of LibreOffice in parallel, perhaps not in Windows or Mac. Presently I have the installation files in /opt/: 6.2, 6.3, 6.3.4. and 6.4. I can run all four at the same time if I so desire.
How did I do this? all but 6.3.4 were installed normally with one exception: I changed the last line in bootstraprc using a text editor as an administrator.
UserInstallation=$SYSUSERCONFIG/libreoffice/4 became UserInstallation=$SYSUSERCONFIG/libreoffice/6.3 for LibreOffice 6.3. Obviously the end of this line for each of the other versions was 6.2, or 6.4 respectively. When a particular version was first started, the configuration folder is created as a subfolder of /home/.config/
For version 6.3.4, this was more involved. First I followed the link that you have mentioned to install this version in parallel within the folder containing the installation files. (LibreOffice_6.3.4.1_Linux_x86-64_deb/DEBS/Install. This created as a subfolder libreoffice6.3/ which is its installation folder. Then I also followed the same instructions to install the help files for this version in parallel. Next I moved the help folder to the libreoffice6.3 installation folder (/home/username/.config/libreoffice/) which made the help files available to this parallel version of 6.3.4 when it is run.
Next to the last step: Modify the bootstraprc last line to
UserInstallation=$SYSUSERCONFIG/libreoffice/4 became UserInstallation=$SYSUSERCONFIG/libreoffice/Direct. (I wanted to use this particular version to connect to MySQL using the direct connection. Other versions are either using either connecting to MySQL using JAVA or connecting to HSQLDB 2.5.0.)
Last step: As administrator, I moved the libreoffice6.3 folder that I had created to the /opt/ folder.
There may well be something listed here that could be used for Windows or Mac, I do not know.
Dan