I have the same issue so wanted to debug. But this is confusing…
WP Real Media Library is active (as in – I can deactivate AND I see a folder structure in Media)
But I get this warning:
The plugin Real Media Library is not active (maybe not installed neither) or the version of Real Media Library is < 2.8.3 (please update). However, you activated the WP/LR Sync extension for it. Until the plugin is installed, the extension will not be loaded.
And I was in fact looking for an answer if, when checking extension Real Media Library, if it still is recommended to check ‘post types’