Open Source: No
Link to source tarball/zip file: https://www.mendeley.com/download-mendeley-desktop/linux64/instructions/
We already have Mendeley in 3rd-party: https://wiki.solus-project.com/3rdParty#Mendeley_Desktop
it does't work exactly. for example, libreoffice plugin does not work.
If something doesn't work as intended, you can also file a separate request. @hanshenden