Naive aside, but why would I want to use ElasticSearch or OpenSearch over Solr? Are ES and Solr not both based on Lucene?
I haven't extensively used ES, but I've used Solr a lot (and contributed to), and I can say that it's a mess. The community is not one of the better ones I've seen. Bugs and stability issues are often ignored. Patches sit around gathering dust. There are some gems and very clever people in the community, of course, but it seems like there are too few of them to cope with the large beast that Solr has become. If I were starting a new project in the search space, Solr would not make my shortlist.
Other benefit is that you don't have to rely on Zookeeper if you're horizontally scaling.
I don't have a ton of experience with Solr but they seem pretty comparable.
IIRC Solr also has some weird stuff about schemaless indices, whereas ES took the very Mongo-y approach of "yeah, just throw content at the index, don't worry about it" but then separately the approach of "I am angry with your new conflicting field in that document" and throws an exception; so you don't have to worry about the schema right up until you do have to worry about it
I'd probably use ES for any log analytics and Solr for things like website and ecommerce search.
Of course, you could do both with either.