I used the A7iii for a while, and I like the Rokinon 8mm a lot with it for filming. You can film 4:3 with it, or you can use Clear Image Zoom to crop in and get a 16:9 image. That way you can set the vigentte where you want, or have none at all.
That said, it's not great for photography because you'd have to crop it. If you want something that does hybrid photo/video really well, you want the canon 8-15 or the new Laowa 8-15 probably. If you're mainly filming, the 8mm is an affordable workhorse in my opinion