This is probably due to #35287 where additional columns are rendered. This likely leads to additional SQL queries.

I don't have a reference prior to the upgrade, but on my (production) machine with Foreman 3.5.0-rc2 it takes about 800ms to render (and send) the host index page HTML. Then it still needs to render on my browser etc. That feels way slower than it was before.

Looking in production.log I see a lot of allocations, which often is because of many SQL queries. It's likely that the reported data facets are retrieved one by one instead of in a single batch.