Sphinx search is an awesome search backend. The challenge is it requires installing and running the sphinx daemon, which generally cannot be done on shared hosting plans.
As to the specific version question, look for guidance on the
Sphinx Downloads | Open Source Search Server page
Sphinx "open source" wrote: 3.0 and up sources are currently only available under a delayed FOSS or commercial licenses for several reasons; going back to regular plain old GPL is planned but timing is moot; so email us if you require the sources immediately.
Sources for previous 2.x versions can be found either in the Archive below or on GitHub, github.com/sphinxsearch/sphinx
From some previous research notes an alternative might be
About Manticore Search Manticore Search wrote:Manticore Search is an open-source database that was created in 2017 as a continuation of Sphinx Search engine. We took all the best from it, significantly improved its functionality, fixed hundreds of bugs, rewrote the code almost completely and kept it open-source! That all has made Manticore Search a modern, fast, light-weight and full-featured database with outstanding full-text search capabilities.
Clearly there is some backstory involved. I have no clue on the details although there are many clues in the blog post
Jul 24, 2017. Sphinx 2017.
Normal people… believe that if it ain’t broke, don’t fix it. Engineers believe that if it ain’t broke, it doesn’t have enough features yet. – Scott Adams