Just to clarify, the WP Discourse Plugin has no issues with the latest Discourse. You can see the plugin working with a Discourse instance that is automatically updated to the latest Discourse version every 24 hours here: https://try.thepavilion.io/c/wordpress/21. The Discourse it is connected to is here: wordpress.thepavilion.io
Apologies if you mentioned this, but just checking you’re also updating the Discourse URL in the WP Discourse plugin’s connection settings?