You need to disable and remove aspects of world partition for your level before you can uncheck that setting. All of this is contained in world settings, so I’ll mention what settings to change and you can search for them. Note that you will have to do this for any level that’s created using the open world preset.
Uncheck Enable Streaming
Click the Disable button next to Disable World Partition
Uncheck Use External Actors, this will require you save your level
Use External Actors - unchecked
The options in step 2 and 3 can not be found in World Settings.
Is still checked and it can not be unchecked.
edit: The above situation can be reproduced with the 3rd person template in UE 5.1.1
The above solution steps work on UE 5.3.1 .
The video Physics Objects | GameDev.tv is unclear if it switched to the new version or something else was done behind the scenes.
It’s possible that I tried these steps in a version that wasn’t 5.1 by accident last night without paying attention to that particular detail.
I’m investigating the solution for 5.1 specifically (as documentation is not clear on what causes that option to be greyed out). Though in the meantime this should not cause an issue when following the course.
Edit: Looks like the steps I outlined were introduced in UE 5.2 and that the ability to disable World Partition once it’s enabled for a level (which is the default for the levels used in the Third-Person and First-Person projects) is not possible in 5.0.3 and 5.1.1. However, you can create a new blank level without world partition by going to File -> New Level -> Blank.