How to parse a message for keywords to find similar topics?

Question

Search Engine Optimization

Greetings!
I want topics to be automatically selected for the post on the site by the type "read more" or "similar topics", without the need for manual selection.
The main task is to somehow find keywords in the current record and search for them through Elasticsearch. Please tell me how this can be done (algorithm).
For now, I’m thinking of using some library for morphological analysis to parse the record, find all the nouns and search for them, but maybe there is a more correct solution in conjunction with Elastic.