It is likely that the next Obsidian Entertainment project, which is called AVOWED, is developed on the Unreal Engine 5 engine. The information hinting at this information was seen by the Reddit user on the LINKEDIN page Obsidian Entertainment Aaron Dubis, which is just and is working on AVWEDED.
Another confirmation of this theory is that Obsidian Entertainment was mentioned in the list of studios, which are working with Unreal Engine 5 right now as part of a recent presentation in honor of the release of the new version of the engine.