>>366340725fps means 25 frames per second.
You can't shoot at 25 frames per second and have each frame expose for longer than 1/25th of a second.
Like, okay, imagine you have a 12 inch sub sandwich. I tell you that I want you to cut it into four pieces, and that I want each slice to be half of a sandwich. You see how that's not possible, right? There's just not enough sandwich there. It's not a technical limitation we're talking about, it's a physical limitation of reality.
There might be a way to fake it, like what
>>3663091 and
>>3663085 said, but there's not a way to do it on the GH5 or any other camera.