I think you are mistaken and have missed the recent news which OP is about, but I'm not totally sure what you are talking about.

Which license do you consider an OSS licensed elasticsearch?

The apache license, https://github.com/elastic/elasticsearch/blob/master/LICENSE...

If you don't use any of the x-pack features (which used to be paid) you're all good.

Not quite. Elastic is removing Apache licensing altogether for ES and Kibana from 7.11 and switching them to SSPL (or alternately the Elastic license based on user's choice) [1].

[1] : https://www.elastic.co/blog/licensing-change

Oh okay, missed it, thanks!