Even going into the console and running curl -X GET "ipOfElastic:portOfElastic/_search?q=search_term" returns nothing that resides on group folders. Which means the command /occ fulltextsearch:index is not indexing group folders at all.
Also tested with a diferent environment: Nextcloud AIO (container) 30.0.0 + elastic (separated container) 7.17.12, same behavior.
Afeter some more testing I realised that:
The files that were already on group folders prior to the first indexation proccess won’t ever be indexed. Files CREATED into group folders AFTER the indexation process, do get indexed. Moving the files (that were inside group folders prior to the initial indexation) out and in the group folders won’t matter, files won’t get indexed.