Is there a way to handle focusing when you're filming yourself? I'm trying to film myself sitting on a sofa talking.

The problem is, with auto-focus, occasionally the camera can lose focus, for example if I lean forward or back or gesture.

What I want to do is auto focus at the start then simply keep the focus fixed.

I can put my camera into manual focus, but since I'm not in the picture on the sofa, I can't really focus it.

Do I have to put a dummy object where I would sit in order to manually focus? Or is there a better technique than this?

I'm asking as a camera-agnostic question, but I have a panasonic lumix g90 which has a physical dial for choose auto-focus modes or manual. I tried using the app to remotely control it, but I guess as it's a dial, I can't change it? Also since I can't see the screen while I'm sat down, focusing it using an app would be quite tricky anyway.

I figure this is a common enough situation to have a solution to it, if anyone has any ideas.
Put a dummy object where you will sit, and focus on that.

With a dedicated video camera, you would normally zoom in on the focus point, set the focus, and then zoom out again for your desired framing. Your camera appears to be a stills camera, and my understanding is that the lenses on a stills camera don't work the same way as the zoom lens on a video camera, so that particular technique might not be applicable (hopefully someone with stills camera experience can jump in here). But definitely set the framing/focus on a dummy object where you will be, and lock that.

If you are going slightly in/out of focus with your movement, you could move the camera further back as well - the further back the camera is from you, the more depth of field (range of focus distance) you will have on the object being focused on. The trade off being that as you move the camera further away, the sharpness of the image may decrease, the more zoom you are using - although you're unlikely to move the camera far enough back in your setup to make a noticeable difference.